SECTION 8 CLOCKS AND POWER CONTROL
Contents
1. Ps Figure 8 4 MPC555 Clocks Note that GCLK1 50 GCLK2 50 and CLKOUT can have a lower frequency than GCLK1 and GCLk2 This is to enable the external bus operation at lower frequencies controlled by EBDF in the SCCR GCLK2 50 always rises simultaneously with MPC555 USER S MANUAL MOTOROLA 8 7 CLOCKS AND POWER CONTROL Revised 15 September 1999 ja GCLK2 When DFNH 0 GCLK2 50 has a 50 duty cycle With other values of DFNH or DFNL the duty cycle is less than 50 Refer to Figure 8 7 GCLK1 50 rises simultaneously with GCLK1 When the MPC555 is not in gear mode the falling edge of GCLK1 50 occurs in the middle of the high phase of GCLK2 50 EBDF determines the division factor between GCLK1 GCLK2 and GCLK1 50 GCLK2 50 During power on reset the MOCCK1 MODCK2 and MODCK3 pins determine the clock source for the PLL and the clock drivers These pins are latched on the positive edge of PORESET Their values must be stable as long as this line is asserted The configuration modes are shown in Table 8 12. COLIR Change of Lock Interrupt Register 0x2F C28C MSB LSB 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 COLIRQ COLIS COLIE RESET 0 0 0 0 0 0 0 0 0 U U U U U U U Unaffected by reset MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 34 Table 8 11 COLIR Bit Settings Bit s Name Description Change of lock interrupt request level These bits determine the interrupt priority level of the d BOERS change of lock To specify certain level the appropriate one of these bits should be set If set one the bit indicates that a change in the PLL lock status was detected The PLL 8 COLIS was locked and lost lock or the PLL was unlocked and got locked The bit should be cleared by writing a one Change of Lock Interrupt enable If COLIE bit is asserted an interrupt will generate when the COLIS bit is asserted 3 See 0 Change of lock Interrupt disable 1 Change of lock Interrupt enable 10 15 Reserved 8 12 4 VDDSRAM Control Register VSRMCR This register contains control bits for enabling or disabling the VDDSRAM supply detection circuit There are also four bits that indicate the failure detection All four bits have the same function and are required to improve the detection capability in extreme cases VSRMCR VDDSRAM Control Register Ox2F C290 MSB LSB 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 LVSRS VSRDE RESERVED HAR
3. 8 2 System Clock Sources The system clock can be provided by the main system oscillator OSCM an external clock input or the backup clock BUCLK on chip ring oscillator see Figure 8 2 The OSCM uses either a 4 MHz or 20 MHz crystal to generate the PLL reference clock When the main system oscillator output is the timing reference to the system PLL skew elimination between the XTAL EXTAL pins and CLKOUT is not guaranteed The external clock input receives a clock signal from an external source The clock fre quency must be either in the range of 3 MHz 5 MHz or at the system frequency of at least 15 MHz 1 1 mode When the external clock input is the timing reference to the system PLL skew elimination between the EXTCLK pin and the CLKOUT is less than t1ns The backup clock on chip ring oscillator enables the MCU to function with a less pre cise clock When operating from the backup clock the MCU is in limp mode This enables the system to continue minimum functionality until the system is fixed The BUCLK frequency is approximately 7 MHz see APPENDIX G ELECTRICAL CHAR ACTERISTICS for the complete frequency range For normal operation at least one clock source EXTCLK or OSCM must be active A configuration with both clock sources active is possible as well At this configuration EXTCLK provides the OSCCLK and OSCM provides the PITRTCLK The input of an unused timing reference EXTCLK or EXTAL must be grounded XTAL
4. Bit s Name Description TMIST Timers interrupt status TMIST is set when an interrupt from the RTC PIT TB or DEC occurs The TMIST bit is cleared by writing a one to it Writing a zero has no effect on this bit The system clock frequency remains at its high frequency value defined by DFNH if the TMIST bitis set even if the CSRC bit in the PLPRCR is set DFNL enabled and conditions to switch to normal low mode do not exist This bit is cleared during power on or hard reset 0 No timer expired event was detected 1 Atimer expire event was detected 20 Reserved 21 CSRC Clock source This bit is cleared at hard reset 0 General system clock is determined by the DFNH value 1 General system clock is determined by the DFNL value 22 23 LPM Low power mode select These bits are encoded to provide one normal operating mode and four low power modes In normal and doze modes the system can be in high state fre guency determined by the DFNH bits or low state freguency defined by the DFNL bits The LPM field can be write protected by setting the LPM and CSRC lock LPML bit in the PLPRCR Refer to Table 8 4 and Table 8 5 24 CSR Checkstop reset enable If this bit is set then an automatic reset is generated when the RCPU signals that it has entered checkstop mode unless debug mode was enabled at reset If the bit is clear and debug mode is not enabled then the USIU will not do anything upon r
5. DIVF 1 NOTE When operating with the backup clock the system clock and CLK OUT is one half of the ring oscillator freguency i e the system clock is a nominal 7 MHz The time base and PIT clocks will be twice the system clock freguency MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 4 The PLL maximum lock time is determined by the input clock to the phase detector The PLL locks within 500 input clock cycles NOTE Upon initial system power up and after KAPWR is lost an external circuit must assert power on reset PORESET If limp mode will be enabled during power on reset PORESET must be asserted for at least 100 000 cycles of input PLL clock after a valid level has been reached on the KAPWR supply If limp mode will be disabled PORESET should be asserted for approximately 3 us after a valid level has been reached on the KAPWR supply Whenever power on reset is asserted the MF bits are set according to Table 8 1 and the DFNH and DFNL bits in SCCR are set to the value of 0 1 and 2 respectively XFC U 1 B Charge Pump Division Factor DIVF 0 4 OSCCLK gt VCOOUT Down Feedback Phase Comparator Clock Multiplication Factor Figure 8 3 System PLL Block Diagram 8 3 5 PLL Pins The following pins are dedicated to the PLL operation e VDDSYN Drain voltage This is the VDD dedicated to the analog PLL circuits The voltage should
6. EXTAL O E TU Resistor is not currently reguired on the board but space should be available for its addition in the future Figure 8 2 Main System Oscillator OSCM 8 3 System PLL The PLL allows the processor to operate at a high internal clock frequency using a low frequency clock input a feature which offers two benefits Lower frequency clock input reduces the overall electromagnetic interference generated by the system and the ability to oscillate at different frequencies reduces cost by eliminating the need to add an additional oscillator to a system The PLL can perform the following functions Frequency multiplication Skew elimination MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 3 Frequency division 8 3 1 Frequency Multiplication The PLL can multiply the input frequency by any integer between one and 4096 The multiplication factor depends on the value of the MF 0 1 1 bits in the PLPRCR register While any integer value from one to 4096 can be programmed the resulting VCO out put frequency must be at least 15 MHz The multiplication factor is set to a predetermined value during power on reset as defined in Table 8 1 8 3 2 Skew Elimination The PLL is capable of eliminating the skew between the external clock entering the chip EXTCLK and both the internal clock phases and the CLKOUT pin making it use ful for tight synchronous timings Sk
7. LPM and CSRC bits are locked and hard reset will occur if the MCU is not in normal high mode Time base source Note that when the chip is operating in limp mode BUCS 1 TBS is ignored and the backup clock is the time base clock source 0 Source is OSCCLK divided by either four or 16 1 Source is system clock divided by 16 RTC and PIT clock divider At power on reset this bit is cleared if MODCK 1 3 are all low 7 RTDIV otherwise the bit is set 0 RTC and PIT clock divided by four 1 RTC and PIT clock divided by 256 Switch to backup clock control When software sets this bit the system clock is switched to the on chip backup clock ring oscillator and the chip undergoes a hard reset The STBUC 8 STBUC bit is ignored if LME is cleared 0 Do not switch to the backup clock ring oscillator 1 Switch to backup clock ring oscillator 9 Reserved Power management request enable 0 Remains in the lower frequency defined by DFNL even if the power management bit in the MSR is reset normal operational mode or if there is a pending interrupt from the 10 PRQEN interrupt controller 1 Switches to high frequency defined by DFNH when the power management bit in the MSRis reset normal operational mode or there is a pending interrupt from the interrupt controller RTC circuit input source select At power on reset RTSEL receives the value of the MODCK 1 bit Note that if the chip is opera
8. MODCK1 specifies the input source to the SPLL OSCM or EXTCLK MODCK1 MODCK2 and MODCKGS together deter mine the multiplication factor at reset and the functionality of limp mode If the configuration of PITRTCLK and TMBCLK and the SPLL multiplication factor is to remain unchanged in power down low power mode the MODCK signals should not be sampled at wake up from this mode In this case the PORESET pin should remain negated and HRESET should be asserted during the power supply wake up stage When MODCK 1 is cleared the output of the main oscillator OSCM is selected as the input to the SPLL When MODCK 1 is asserted the external clock input EXTCLK is selected as the input to the SPLL In all cases the system clock frequency fredgcik2 can be reduced by the DFNH 0 2 bits in the SCCR Note that freqgcik2 max occurs when the DFNH bits are cleared The TBS bit in the SCCR selects the time base clock to be either the SPLL input clock or GCLK2 When the backup clock is functioning as the system clock the backup clock is automatically selected as the time base clock source The PITRTCLK frequency and source are specified by the RTDIV and RTSEL bits in the SCCR When the backup clock is functioning as the system clock the backup clock is automatically selected as the time base clock source When the PORESET pin is negated driven to a high value the MODCK1 MODCk2 and MODCK3 values are not affected They remain the same as they wer
9. a a gt Figure 8 13 No Standby No KAPWR All System Power On Off MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 26 BuitutueiFoid 9 13534H d 13S3HOd ddA NASAGA VAGA INVHSQGA 8 27 Other Power On Off CLOCKS AND POWER CONTROL Revised 15 September 1999 Figure 8 14 Standby and KAPWR USER S MANUAL MPC555 NOTE The following notes apply to Figure 8 13 and Figure 8 14 above a 1 VDDH gt VDDL 0 35 V 0 5 V max at temperature extremes VPP lt VDDH 0 5 V AND VPP gt VDDL 0 35 V The delta VPP VDDL must be x 3 6 V during power on or off VDDA can lag VDDH and VDDSYN can lag VDDL but both must be at a valid level before resets are negated 2 If keep alive functions are NOT used then when system power is on KAPWR VDDSRAM VDDL 0 35 V 3 If keep alive functions ARE used then KAPWR VDDSRAM VDDL 3 3 V 0 35 V when system power is on VDDSRAM gt 1 8 V and optionally KAPWR 3 3 V 0 3 V when system power is off Normal system power is defined as VDDL VDDI VDDF VDDSYN VPP VDDSRAM KAPWR 3 3 0 3 V and VDDA VDDH 5 0 0 5V Flash Programming requirements are the same as normal system power except VPP 5 0 0 25 V Do
10. and DEC SRAM VDDSRAM detector VDDSRAM VSRMCR KAPWR The following are the relations between different power supplies VDDL VDDI VDDSYN VDDF 3 3 V 10 e KAPWR 2 VDDL 0 2 V during normal operation VDDSRAM 2 VDDL 0 3 V during normal operation VDDSRAM 2 1 4 V during standby operation e VPP 2 VDDL 0 3 V but VPP VDDL lt 4 0 volts 8 9 2 Chip Power Structure The MPC555 provides a wide range of possibilities for power supply connections Fig ure 8 10 illustrates the different power supply sources for each of the basic units on the chip 8 9 2 1 VDDL The I O buffers and logic are fed by a 3 3 V power supply 8 9 2 2 VDDI VDDI powers the internal logic of the MPC555 nominally 3 3 V MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 20 8 9 2 3 VDDSYN VSSSYN The charge pump and the VCO of the SPLL are fed by a separate 3 3 V power supply VDDSYN in order to improve noise immunity and achieve a high stability in its output frequency VSSSYN provides an isolated ground reference for the PLL 8 9 2 4 KAPWR The oscillator time base counter decrementer periodic interrupt timer and the real time clock are fed by the KAPWR rail This allows the external power supply unit to disconnect all other sub units of the MCU in low power deep sleep mode The TEXP pin fed by the same rail can be used by the external power supply unit to switch between sour
11. be well regulated and the pin should be provided with an ex tremely low impedance path to the VDD power rail VDDSYN should be bypassed to VSSSYN by a 0 1 capacitor located as close as possible to the chip pack age VSSSYN Source voltage This is the VSS dedicated to the analog PLL circuits The pin should be provided with an extremely low impedance path to ground VSSSYN should be bypassed to VDDSYN by a 0 1 pF capacitor located as close as possible to the chip package XFC External filter capacitor XFC connects to the off chip capacitor for the PLL filter One terminal of the capacitor is connected to XFC and the other termi nal is connected to VDDSYN The off chip capacitor must have the following values preliminary MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 5 EI O lt MF 1 lt 4 680 x MF 1 120 pF MF 1 gt 4 1100 x MF 1 pF a Where MF the value stored on MF 0 11 This is one less than the desired frequency multiplication 8 4 System Clock During PLL Loss of Lock At reset until the SPLL is locked the SPLL output clock is disabled During normal operation once the PLL has locked either the oscillator or an external clock source is generating the system clock In this case if loss of lock is detected and the LOLRE loss of lock reset enable bit in the PLPRCR is cleared the system clock source continues to function as the PLL s output clock The USIU
12. changed by software The RTDIV bit value in the SCCR register defines the division of PITRTCLK All possible combinations of the TMBCLK divisions are listed in Table 8 2 Table 8 2 TMBCLK Divisions SCCR TBS MF 1 dst 1 16 0 1 2 16 0 gt 2 4 8 6 1 General System Clocks The general system clocks GCLK1C GCLK2C GCLK1 GCLK2 GCLK1 50 and GCLK2 50 are the basic clock supplied to all modules and sub modules on the MPC555 GCLK1C and GCLK2C are supplied to the RCPU and to the BBC GCLK1C MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 9 and GCLK2C are stopped when the chip enters the doze low power mode GCLK1 and GCLK2 are supplied to the SIU and the clock module The external bus clock x1 GCLK2 50 is the same as CLKOUT The general system clock defaults to VCO 2 20 MHz assuming a 20 MHz system frequency with default power on reset MF values The general system clock frequency can be switched between different values The highest operational frequency can be achieved when the system clock frequency is determined by DFNH CSRC bit in the PLPRCR is cleared and DFNH 0 division by one The general system clock can be operated at a low frequency gear mode or a high frequency The DFNL bits in SCCR define the low frequency The DFNH bits in SCCR define the high frequency The frequency of the general system clock can be changed dynamically with the sys te
13. for an optimized low power system SW1 and SW can be unified in only one switch if VDDSYN and VDDI VDDL are supplied by the same source MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 22 3 VDDSYN i Supply i i 3 3 V 1 1 O SW2 VDD r MPC555 VDDSRAM Power Supply Figure 8 11 External Power Supply Scheme The MPC555 asserts the TEXP signal if enabled when the RTC or TB time value matches the value programmed in the associated alarm register or when the PIT or DEC value reaches zero The TEXP signal is negated when the TEXPS status bit is written to one The KAPWR power supply feeds the main crystal oscillator OSCM The condition for the main crystal oscillator stability is that the power supply value changes slowly The maximum slope must be less than 5 mV per oscillation cycle t gt 200 300 fregysem 8 9 3 2 Keep Alive Power Registers Lock Mechanism The USIU timer clocks reset power decrementer and time base registers are pow ered by the KAPWR supply When the main power supply is disconnected after power down mode is entered the value stored in any of these registers is preserved If power down mode is not entered before power disconnect there is a chance of data loss in these registers To minimize the possibility of data loss the MPC555 includes a key mechanism that ensures dat
14. information detailing the functionality of the VPP signal for flash program and erase is outlined in 19 9 2 FLASH Program Erase Voltage Conditioning Power consumption during power up sequencing can not be specified prior to evaluation and characterization of production silicon The goal is to keep the power consumption during power up sequencing below the operating power consumption During the power down sequence the user needs to assert PORESET while VDDI and VDDL are at a voltage equal or greater to 3 V Below this voltage the power supply chip can be turned off If the turn off voltage of the power supply chip is greater than 0 74 V for the 3 V supply and greater than 0 8 V for the 5 V supply then the circuitry inside the MPC555 will act as a load to the respective supply and will discharge the supply line down to these values Since the 3 V logic represents a larger load to the supply chip the 3 V supply line will decay faster than the 5 V supply line MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 25 O re o a 2 gt a o E o E 2 E c Oo 9 o z 3 E c o 2 5 z S E o 5 2 e I I z 8 a a z lt c gt e Lr a a a rs o a 0 gt gt lt 0 77 zi a lt a a gt o f gt gt
15. not hold the 3 V supplies at ground while VDDH VDDA is ramping to 5 V If 5 V is applied before the 3 V supply all 5 V outputs will be in indeterminate states until the 3 V supply reaches a level that allows reset to be distributed throughout the device o gt 8 12 Clocks Unit Programming Model MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 28 8 12 1 System Clock Control Register SCCR The SPLL has a 32 bit control register SCCR which is powered by keep alive power SCCR System Clock Control Register Ox2F C280 MSB 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 DBCT COM DCSLR MFPDL LPML TBS RTDIV STBUCRESERVEDPRQENIRTSEL BUCS EBDF LME POWER ON RESET 1 0 0 0 0 0 0 1 0 0 1 EQ2 EQ3 HARD RESET U 0 ID2 U 0 0 U U U 0 1 U U ID 13 14 U LSB 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 EECLK ENGDIV DFNL x DFNH POWER ON RESET 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 HARD RESET U U U U U U U U 0 0 0 0 0 0 0 Note 1 RTDIV will be 0 if MODCK 1 3 06000 EQ2 MODCK1 EQ3 MODCK1 8 MODCK2 amp MODCK3 MODCK1 amp MODCK2 amp MODCK3 MODCK1 8 MODCK2 8 MODCK3 See Table 8 1 The hard reset value is a reset configuration word value extracted from the indicated internal data bus lines Refer to 7 5 2 Hard Reset Configuration Word U Unaffected by reset Table 8 9 SCCR Bit Settings Bit s Na
16. sleep Interrupt 125 usec 4 MHz 25 usec 20 MHz lt 500 oscillator cycles power supply wake up Power down Interrupt VDDSRAM External Power on seguence 8 8 3 1 Exiting from Normal Low Mode In normal mode as well as doze mode if the PLPRCR CSRC bit is set the system toggles between low frequency defined by PLPRCR DFNL and high frequency defined by PLPRCR DFNH The system switches from normal low mode to normal high mode if either of the following conditions is met An interrupt is pending from the interrupt controller or The MSR POW bit is cleared power management is disabled When neither of these conditions are met the PLPRCR CSRC bit is set and the asyn chronous interrupt status bits are reset the system returns to normal low mode MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 17 8 8 3 2 Exiting from Doze Mode The system changes from doze mode to normal high mode whenever an interrupt is pending from the interrupt controller 8 8 3 3 Exiting from Deep Sleep Mode The system switches from deep sleep mode to normal high mode if any of the follow ing conditions is met An interrupt is pending from the interrupt controller An interrupt is requested by the RTC PIT or time base A decrementer exception In deep sleep mode the PLL is disabled The wake up time from this mode is up to 500 PLL input frequency clocks In one to
17. that the GCLKs generated by this division fac 8 12 2 PLL Low Power and Reset Control Register PLPRCR The PLL low power and reset control register PLPRCR is a 32 bit register powered by the keep alive power supply PLPRCR PLL Low Power and Reset Control Register Ox2F C284 MSB 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 MF RESERVED LOCS LOCSS SPLS POWER ON RESET OOR4 0 0 0 0 HARD RESET U U U U U U U U U U U U U U U U LSB 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 SPLSS TEXPS RESERVED TMIST RESERVED CSRC LPM CSR LOLRE RESERVED DIVF POWER ON RESET 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 HARD RESET U 1 U 0 U 0 0 0 U U U U U U U U Unaffected by reset MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 32 Table 8 10 PLPRCR Bit Settings Bit s Name Description Multiplication factor bits The output of the VCO is divided to generate the feedback signal to the phase comparator The MF bits control the value of the divider in the SPLL feedback loop The phase comparator determines the phase shift between the feedback signal and the reference clock This difference results in either an increase or decrease in the VCO out put frequency 0 11 MF The MF bits can be read and written at any time However this field can be write protected by setting the MF and pre divider lock MFPDL bit in the Changing the
18. timers can operate with the input clock to the PLL so that these timers are not affected by the PLL loss of lock Software can use these timers to measure the loss of lock period If the timer reaches the user preset software criterion the MCU can switch to the backup clock by setting the switch to backup clock STBUC bit in the SCCR provided the limp mode enable LME bit in the SCCR is set If loss of lock is detected during normal operation assertion of HRESET for example if LOLRE is set disables the PLL output clock until the lock condition is met During hard reset the STBUC bit is set as long as the PLL lock condition is not met and clears when the PLL is locked If STBUC and LME are both set the system clock switches to the backup clock and the chip operates in limp mode until STBUC is cleared Every change in the lock status of the PLL can generate a maskable interrupt NOTE When the VCO is the system clock source chip operation is unpre dictable while the PLL is unlocked Note further that a switch to the backup clock is possible only if the LME bit in the SCCR is set 8 5 Low Power Divider The output of the PLL is sent to a low power divider block In limp mode the BUCLK is sent to a low power divider block This block generates all other clocks in normal operation but has the ability to divide the output frequency of the VCO before it gen erates the general system clocks sent to the rest of the MPC555 The PLL VCOOU
19. which sets the LOCS status bit and LOCSS sticky bit in the PLPRCR If the LME bit in the SCCR is set whenever LOCS is asserted the clock logic switches the system clock automatically to BUCLK and asserts hard reset to the chip Switching the system clock to BUCLK is also possible by software setting the STBUC bit in SCCR Switching from limp mode to normal sys tem operation is accomplished by clearing STBUC and LOCSS bits This operation also asserts hard reset to the chip At HRESET assertion if the PLL output clock is not valid the BUCLK will be selected until software clears LOCSS bit in SCCR At HRESET assertion if the PLL output clock is valid the system will switch to oscillator external clock If during HRESET the PLL loses lock or the clock frequency becomes slower than the required value the system will switch to the BUCLK After HRESET negation the PLL lock condition does not effect the system clock source selection If the LME bit is clear the switch to the backup clock is disabled and assertion of STBUC bit is ignored If the chip is in limp mode clearing the LME bit switches the sys tem to normal operation and asserts hard reset to the chip Figure 8 8 describes the clock switching control logic Table 8 3 summarizes the sta tus and control for each state MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 13 1eseJod 0 d iu 0 q 195910 t LME 1 buclk en
20. D RESET U U U U 0 U Unaffected by reset Table 8 12 VSRMCR Bit Settings Bit s Name Description 0 Reserved Loss of VDDSRAM sticky These status bits indicate whether a VDDSRAM supply failure occurred In addition when the power is turned on for the first time VDDSRAM rises and these bits are set The L VSRS bits are cleared by writing them to ones A write of zero has 1 4 LVSRS no effect on these bits 0 No VDDSRAM supply failure was detected 1 VDDSRAM supply failure was detected VDDSRAM detector disable 5 VSRDE 0 VDDSRAM detection circuit is enabled 1 VDDSRAM detection circuit is disabled 6 15 Reserved MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 35 MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 36
21. MF bits causes the SPLL to lose lock Also the MF field should not be modified when entering or exiting from low power mode LPM change or when back up clock is active The normal reset value for the DFNH bits is zero divide by one When the PLL is operating in one to one mode the multiplication factor is set to x1 MF 0 12 Reserved Loss of clock status When the oscillator or external clock source is not at the minimum fre quency the loss of clock circuit asserts the LOCS bit This bit is cleared when the oscillator or external clock source is functioning normally This bit is reset only on power on reset 53 Lesen Writes to this bit have no effect 0 No loss of oscillator is currently detected 1 Loss of oscillator is currently detected Loss of clock sticky If after negation of PORESET the loss of clock circuit detects that the oscillator or external clock source is not at a minimum frequency the LOCSS bit is set LOCSS remains set until software clears it by writing a one to it A write of zero has no effect 14 LOCSS on this bit The reset value is determined during hard reset The STBUC bit will be set pro vided the PLL lock condition is not met when HRESET is asserted and cleared if the PLL is locked when HRESET is asserted 0 No loss of oscillator has been detected 1 Loss of oscillator has been detected System PLL lock status bit 15 SPLS 0 SPLL is currently not locked 1 SPLL is currently lo
22. NGDIV but are cleared during power on reset Note that if the engineering clock division factor is not a power of two synchronization between the system and ENGCLK is not guaranteed 24 Reserved Division factor low frequency The user can load these bits with the desired divide value and the CSRC bit to change the frequency Changing the value of these bits does not result in a loss of lock condition These bits are cleared by power on or hard reset Refer to 8 6 1 Gen eral System Clocks and Figure 8 5 for details on using these bits 000 Divide by 2 25 27 DFNL 001 Divide by 4 010 Divide by 8 011 Divide by 16 100 Divide by 32 101 Divide by 64 110 Reserved 111 Divide by 256 MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 31 Table 8 9 SCCR Bit Settings Continued Bit s Name Description 28 Reserved tor are not 50 duty cycle i e CLKOUT 000 Divide by 1 29 31 DFNH 001 Divide by 2 010 Divide by 4 011 Divide by 8 100 Divide by 16 101 Divide by 32 110 Divide by 64 111 Reserved Division factor high freguency These bits determine the general system clock freguency dur ing normal mode Changing the value of these bits does not result in a loss of lock condition These bits are cleared by power on or hard reset The user can load these bits at any time to change the general system clock rate Note
23. R Bit Settings Continued Bit s Name Description Disable clock switching at loss of lock during reset When DCSLR is clear and limp mode is enabled the chip will switch automaticaly to the backup clock if the PLL losses lock during HRESET When DCSLR is asserted a PLL loss of lock event does not cause clock switch 3 DCSLR ing If HRESET is asserted and DCSLRis set the chip will not negate HRESET until the PLL aquires lock 0 Enable clock switching if the PLL loses lock during reset 1 Disable clock switching if the PLL loses lock during reset MF and pre divider lock Setting this control bit disables writes to the MF and DIVF bits This helps prevent runaway software from changing the VCO frequency and causing the SPLL to lose lock In addition to protect against hardware interference a hardware reset will be 4 MFPDL asserted if these fields are changed while LPML is asserted This bit is writable once after power on reset 0 MF and DIVF fields are writable 1 2 MF and DIVF fields are locked LPM lock Setting this control bit disables writes to the LPM and CSRC control bits In addi tion for added protection a hardware reset is asserted if any mode is entered other than normal high mode This protects against runaway software causing the MCU to enter low 5 LPML power modes The MSR POW bit provides additional protection LPML is writable once after power on reset 0 LPM and CSRC bits are writable 1
24. S AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 24 KAPWR Power On Reset Valid for other registers Open Write to the key other value Figure 8 12 illustrates the process of locking or unlocking a register powered by nl B Write to the Key 0x55CCAA33 Power On Reset AC Valid for RTC RTSEC Locked RTCAL and RTCSC Figure 8 12 Keep Alive Register Key State Diagram 8 10 VDDSRAM Supply Failure Detection A special circuit for VDDSRAM supply failure detection is provided In the case of sup ply failure detection the dedicated sticky bits LVSRS in the VSRMCR register are asserted Software can read or clear these bits The user should enable the detector and then clear these bits If the user reads any of the LVSR bits as one then a power failure of VDDSRAM has occurred The circuit is capable of detecting supply failure below 2 6 V Also enable disable control bit for the VDDSRAM detector may be used to disconnect the circuit and save the detector power consumption 8 11 Power Up Down Sequencing Figure 8 13 and Figure 8 14 detail the power up sequencing for MPC555 during nor mal operation Note that for each of the conditions detailing the voltage relationships the absolute bounds of the minimum and maximum voltage supply cannot be violated i e the value of VDDL cannot fall below 3 0 V or exceed 3 6 V and the value of VDDH cannot fall below 4 5 V or exceed 5 5 V for normal operation Further
25. SECTION 8 CLOCKS AND POWER CONTROL 8 1 Overview The main timing reference for the MPC555 can monitor any of the following Acrystal with a frequency of 4 MHz or 20 MHz An external frequency source with a frequency of 4 MHz An external frequency source at the system frequency The system operating frequency is generated through a programmable phase locked loop the system PLL SPLL The SPLL is programmable in integer multiples of the input oscillator frequency to generate the internal VCO 2 operating frequency A pre divider before the SPLL enables the user to divide the high frequency crystal oscillator The internal operating SPLL frequency should be at least 30 MHz It can be divided by a power of two divider to generate the system operating frequencies In addition to the system clock the clocks submodule provides the following TMBCLK to the time base TB and decrementer DEC PITRTCLK to the periodic interrupt timer PIT and real time clock RTC The oscillator TB DEC RTC and the PIT are powered from the keep alive power supply KAPWR pin This allows the counters to continue to count increment decre ment at the oscillator frequency even when the main power to the MCU is off While the power is off the PIT may be used to signal to the power supply IC to enable power to the system at specific intervals This is the power down wake up feature When the chip is not in power down low power mode the KAPWR is powere
26. T is always divided by at least 2 The purpose of the low power divider block is to allow the user to reduce and restore the operating frequencies of different sections of the MPC555 without losing the PLL lock Using the low power divider block the user can still obtain full chip operation but at a lower frequency This is called gear mode The selection and speed of gear mode can be changed at any time with changes occurring immediately The low power divider block is controlled in the system clock control register SCCR The default state of the low power divider is to divide all clocks by one Thus for a 40 MHz system the general system clocks are each 40 MHz MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 6 8 6 MPC555 Internal Clock Signals The internal clocks generated by the clocks module are shown in Figure 8 4 The clocks module also generates the CLKOUT and ENGCLK external clock signals The PLL synchronizes these signals to each other The PITRTCLK frequency and source are specified by the RTDIV and RTSEL bits in the SCCR When the backup clock is functioning as the system clock the backup clock is automatically selected as the time base clock source and is twice the MPC555 system clock GCLK1 GCLK2 GCLK1 50 EBDF 00 GCLK2 50 EBDF 00 CLKOUT EBDF 00 GCLK1 50 EBDF 01 GCLK2 50 EBDF 01 CLKOUT EBDF 01 T1 T2 T3 T4
27. Table 8 5 describes the power consumption clock frequency and chip functionality for each power mode Table 8 5 Power Mode Descriptions Power Consumption Operation Mode SPLL Clocks 40 MHz Functionality Preliminary Normal high Active Fun 1 2 Watt Full functions not in use Normal low gear Active io 20 mWatt ge ey 2 ki 4 2 DFNL 1 Watt Doze high Active Full 20 mWatt s 0 4 2DFNH watt memory controller Disabled extended Full frequency 20 mWatt Doze low Active DENL 1 core 2 0 4 2 DFNL 1 Watt RCPU BBC FPU Sleep Active Not active 10 mW 4 MHz lt 1 mW Deep sleep Not active Not active 20 MHz lt TBD Enabled RTC PIT TB Temp 50 C and DEC 1 Power down Not active Not active 4 and 20 MHz lt TBD Temperature 50 C SRAM s data VDDSRAM Not active Not active TBD retention NOTES 1 See Electrical Specification for actual values 8 8 3 Exiting from Low Power Modes Exiting from low power modes occurs through an asynchronous interrupt or a synchro nous interrupt generated by the memory controller Any enabled asynchronous interrupt clears the LPM bits but does not change the PLPRCR CSRC bit MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 16 The exit from normal low doze high and low modes and sleep mode to normal high mode is accomplished with the asynchrono
28. a retention as long as a register is locked While a register is locked writes to this register are ignored Each of the registers in the KAPWR region have a key that can be in one of two states open or locked At power on reset the following keys are locked RTC RTSEC MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 23 RTCAL and RTCSC All other registers are unlocked Each key has an address asso ciated with it in the internal memory map A write of 0x55CCAA33 to the associated key register changes the key to the open state A write of any other data to this location changes the key to the locked state The key registers are write only A read of the key register has undefined side effects and may be interpreted as a write that locks the associated register Table 8 8 lists the registers powered by KAPWR and the associated key registers Table 8 8 KAPWR Registers and Key Registers KAPWR Register Associated Key Register Address or SPR Number Register Address Register Time Base Status and Control TBSCR Time Base Status and Control Key 0x2F C200 See Table 6 16 for bit descriptions 0x2F C300 TBSCRK Time Base Reference 0 TBREFO Ox2F C204 See 6 13 4 3 Time Base Reference Reg 0x2F C304 Time Base Reference 0 Key TBREFOK isters for bit descriptions Time Base Reference 1 TBREF1 Ox2F C208 See 6 13 4 3 Time Base Refer
29. able 1 LME amp hreset b 0 9 hreset_b 0 LOCS buclk_enable 0 amp hreset_b 0 buclk_enable 0 amp hreset_b 0 hreset_b 1 0 buclk enable 1 amp hreset_b 0 hresert_b Figure 8 8 Clock Source Flow Chart NOTES BUCLK ENABLE STBUC LOC amp LME lock indicates loss of lock status bit LOCS for all cases and loss of clock sticky bit LOCSS when state 3 is active When BUCLK ENABLE is changed the chip asserts HRESET to switch the system clock to BUCLK or PLL At PORESET negation if the PLL is not locked the loss of clock sticky bit LOCSS is asserted and the chip should operate with BUCLK MPC555 USER S MANUAL CLOCKS AND POWER CONTROL Revised 15 September 1999 MOTOROLA 8 14 The switching from state three to state four is accomplished by clear ing the STBUC and LOCSS bits If the switching is done when the m PLL is not locked the system clock will not oscillate until lock condi tion is met Table 8 3 Status of Clock Source STATE PORESET HRESET LME in aa STBUC BUCS lock 1 0 0 1 0 0 0 1 BUCLK 2 1 0 1 0 1 0 0 1 BUCLK 3 1 1 1 x 0 1 0 1 1 BUCLK 4 1 0 0 1 0 x 0 0 Oscillator 5 1 1 0 1 0 x 0 0 Oscillator 6 1 0 1 0 1 1 0 1 1 BUCLK NOTES 1 At least one of the two bits LOCSS or BUCS must be asserted one in this state 2 X don t care The default value of the LME bit is determin
30. ces The IRQ 6 7 MODCK 2 3 IRQ5 MODCK1 XTAL EXTAL EXT CLK PORESET HRESET SRESET and RSTCONF TEXP input pins are powered by KAPWR Circuits including pull up resisters driving these inputs should be pow ered by KAPWR 8 9 2 5 VDDA VSSA VDDA supplies power to the analog subsystems of the QADC A and QADC mod ules it is nominally 5 0 V VDDA is the ground reference for the analog subsystems 8 9 2 6 VPP VPP supplies the programming and erase voltage for the CMF Flash modules It is nominally 5 0 V for program or erase operations and can be lowered to a nominal 3 3 V for read operations 8 9 2 7 VDDF VSSF VDDF provides internal power to the CMF flash module it should be a nominal 3 3 V VSSF provides an isolated ground for the CMF flash module 8 9 2 8 VDDH VDDH provides power for the 5 V I O operations It is a nominal 5 0 V 8 9 2 9 VDDSRAM VDDSRAM supplies power to the 26 Kbyte SRAM module and the DPTRAM It can be used to keep the contents on the SRAM stable while the rest of the MPC555 is pow ered down for standby operation 8 9 2 10 VSS VSS provides the ground reference for the MPC555 MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 21 E VDDH VDDI VDDL DI VDDSRAM VDDSYN Figure 8 10 Basic Power Supply Configuration 8 9 3 Keep Alive Power 8 9 3 1 Keep Alive Power Configuration Figure 8 11 illustrates an example of a switching scheme
31. cked SPLL lock status sticky bit An out of lock sets the SPLSS bit The bit remains set until soft ware clears it by writing a one to it A write of zero has no effect on this bit The bit is cleared at power on reset This bit is not affected due to a software initiated loss of lock MF change and entering deep sleep or power down mode The SPLSS bit is not affected by hard reset 0 SPLL has remained in lock 1 SPLL has gone out of lock at least once not due to software initiated loss of lock 16 SPLSS Timer expired status bit This bit controls whether the chip negates the TEXP pin in deep sleep mode thus enabling external circuitry to switch off the VDD power down mode When LPM 11 CSRC 0 and TEXPS is high the TEXP pin remains asserted When LPM 11 CSRC 0 and TEXPS is low the TEXPS pin is negated To enable automatic wake up TEXPS is asserted when one of the following occurs The PIT is expired 17 TEXPS The real time clock alarm is set The time base clock alarm is set The decrementer exception occurs The bit remains set until software clears it by writing a one to it A write of zero has no effect on this bit TEXPS is set by power on or hard reset 0 TEXP is negated in deep sleep mode 1 TEXP pin remains asserted always 18 Reserved MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 33 Table 8 10 PLPRCR Bit Settings Continued
32. d to the same volt age value as the voltage of the I O buffers and logic The MPC555 clock module consists of the main crystal oscillator OSCM the SPLL the low power divider the clock generator the system low power control block and the limp mode control block The clock module receives control bits from the system clock control register SCCR change of lock interrupt register COLIR the low power and reset control register PLPRCR and the PLL Figure 8 1 illustrates the functional block diagram of the clock unit MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 1 MODCK 1 3 z P gt 5 X ja EXTCLK gt 2 L e p 2 1 MU VCOOUT 2 1 MUX or SPLL e Lock TBCLK GCLK2 Low GCLK1 GCLK2 A Y Power D 3 1 MUX Dividers J4 or 16 1 2N GCLK1C GCLK2C o Clock M ii Drivers U Oo o 2 S Y CLKOUT Drivers ENGCLK m TMBclk TMBCLK gt Driver Back_Up Clock Oscillator Loss Detector RTC PIT Clock PITRTCLK XTAL and DRIVER Main Clock Oscillator OSCM EXTAL Figure 8 1 Clock Unit Block Diagram MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 2
33. e defined during the most recent power on reset Table 8 1 shows the clock configuration modes during power on reset PORESET asserted MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 8 Table 8 1 Reset Clocks Source Configuration Default Values o PORESET MODCKT 1 3 LME MF i4 PITCLK TMBCLK SPLL Options Division Division 000 0 513 4 4 Used for testing purposes Normal operation PLL enabled 001 0 1 256 16 Main timing reference is freq OSCM 20 MHz Limp mode disabled Normal operation PLL enabled 010 1 5 256 4 Main timing reference is freq OSCM 4 MHz Limp mode enabled Normal operation PLL enabled 011 1 1 256 16 Main timing reference is freq OSCM 20 MHz Limp mode enabled Normal operation PLL enabled 1 1 Mode 100 0 1 256 16 freqclkout max freq EXTCLK Limp mode disabled Normal operation PLL enabled 1 1 Mode 101 0 1 256 16 freqclkout max freq EXTCLK Limp mode disabled Normal operation PLL enabled 110 0 5 256 4 Main timing reference is freq EXTCLK 3 5 MHz Limp mode disabled Normal operation PLL enabled 1 1 Mode 111 1 1 256 16 freqclkout max freq EXTCLK Limp mode enabled NOTES 1 For other implementations in the MPC500 family MODCK2 could be inverted NOTE The reset value of the PLL pre divider is 1 The values of the PITRTCLK clock division and TMBCLK clock division can be
34. eceiving the checkstop signal from the RCPU If debug mode is enabled then the part enters debug mode upon entering checkstop mode In this case the RCPU will not assert the checkstop signal to the reset circuitry This bit is writable once after soft reset 0 No reset will occur when checkstop is asserted 1 Reset will occur when checkstop is asserted 25 LOLRE Loss of lock reset enable 0 Loss of lock does not cause HRESET assertion 1 Loss of lock causes HRESET assertion Note if limp mode is enabled use the COLIR feature instead of setting the LOLRE bit See 8 12 3 Change of Lock Interrupt Register COLIR 26 Reserved 27 31 DIVF The DIVF bits control the value of the pre divider in the SPLL circuit The DIVF bits can be read and written at any time However the DIVF field can be write protected by setting the MF and pre divider lock MFPDL bit in the SCCR Changing the DIVF bits causes the SPLL to lose lock 8 12 3 Change of Lock Interrupt Register COLIR The COLIR is 16 bit read write register It controls the change of lock interrupt gener ation and is used for reporting a loss of lock interrupt source It contains the interrupt request level and the interrupt status bit This register is readable and writable at any time A status bit is cleared by writing a one writing a zero does not affect a status bit s value The COLIR is memory mapped into the MPC555 USIU register map
35. ed LPM 11 CSRC 0 by External Hard Reset TEXPS 0 7 or External Hard Reset Software Hard Reset Software is active only in normal high low modes Wake up 3 4 SysFreq gt Clocks Asynchronous Software Doze High Interrupts LPM 01 CSRC 0 1 Wake up 3 4 SysFreqmax Clocks Normal High Mode LPM 00 CSRC 0 1 W y x TEXPS receives the zero value by writing one Writing of zero has no effect on TEXPS The switch from normal high to normal low is enable only if the conditions to asynchronous interrupt are cleared Figure 8 9 MPC555 Low Power Modes Flow Diagram MPC555 CLOCKS AND POWER CONTROL USER S MANUAL Revised 15 September 1999 MOTOROLA 8 9 Basic Power Structure 8 9 1 Clock Unit Power Supply KAPWR and VSS power the following clock unit modules oscillator PITRTCLK and TMBCLK generation logic timebase decrementer RTC PIT system clock control register SCCR low power and reset control register PLPRCR and reset status register RSR All other circuits are powered by the normal supply pins VDDI VDDL VDDH and VSS The power supply for each block is listed in Table 8 7 Table 8 7 Clock Unit Power Supply Circuit Power Supply CLKOUT SPLL digital System low power control VDDL VDDI Internal logic Clock drivers SPLL analog VDDSYN Main oscillator Reset machine Limp mode mechanism Register control SCCR PLLRCR and RSR RTC PIT TB
36. ed by MODCK 1 3 during assertion of the PORESET line The configuration modes are shown in Table 8 1 8 8 Low Power Modes The LPM and other bits in the PLPRCR are encoded to provide one normal operating mode and four low power modes In normal and doze modes the system can be in high state with frequency defined by the DFNH bits or in the low state with frequency defined by the DFNL bits The normal high operating mode is the state out of reset This is also the state of the bits after the low power mode exit signal arrives There are four low power modes Doze mode Sleep mode Deep sleep mode Power down mode 8 8 1 Entering a Low Power Mode Low power modes are enabled by setting the POW bit in the MSR and clearing the LPML low power mode lock bit in the PLPRCR Once enabled a low power mode is entered by setting the LPM bits to the appropriate value This can be done only in one of the normal modes The user cannot change the LPM or CSRC bits when the MCU is in doze mode Table 8 6 summarizes the control bit settings for the different clock power modes MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 15 Table 8 4 Power Mode Control Bit Settings Power Mode LPM 0 1 CSRC TEXPS Normal high 00 0 X Normal low gear 00 1 X Doze high 01 0 X Doze low 01 1 X Sleep 10 X X Deep sleep 11 X 1 Power down 11 X 0 8 8 2 Power Mode Descriptions
37. ence Reg 0x2F C308 Time Base Reference 1 Key TBREF1K isters for bit descriptions Real Time Clock Status and Control Ox2F C220 RTCSC Ox2F C320 Status and Control Key See Table 6 17 for bit descriptions Real Time Clock RTC Ox2F C224 See 6 13 4 6 Real Time Clock Register 0x2F C324 Real Time Clock Key RTCK RTC for bit descriptions ox2F c228 Real Time Alarm Seconds RTSEC 0x2F C328 Real Time Alarm Seconds Key RTSECK Reserved Real Time Alarm RTCAL Ox2F C22C See 6 13 4 7 Real Time Clock Alarm Ox2F C32C Real Time Alarm Key RTCALK Register RTCAL for bit descriptions PIT Status and Control PISCR Ox2F C240 See Table 6 18 for bit descriptions Ox2F C340 PIT Status and Control Key PISCRK PIT Count PITC Ox2F C244 See Table 6 19 for bit descriptions Ox2F C344 PIT Count Key PITCK System Clock Control Register SCCR Ox2F C280 See Table 8 9 for bit descriptions Ox2F C380 System Clock Control Key SCCRK PLL Low Power and Rese Control 0x2F C284 Register PLPRCR 0x2F C384 kis ELBE AL Reset Control Regis See Table 8 10 for bit descriptions y Reset Status Register RSR Ox2F C288 See Table 7 3 for bit descriptions Ox2F C388 Reset Status Register Key RSRK Decrementer SPR 22 See 3 9 5 Decrementer Register DEC for bit descriptions i Tine Ox2F C30C Time Base and Decrementer Key ime Base SPR 268 269 284 285 See Table 3 11 and Table 3 14 for bit de scriptions MPC555 CLOCK
38. ew elimination is active only when the PLL is enabled and programmed with a multiplication factor of one or two MF 0 or 1 The timing reference to the system PLL is the external clock input 8 3 3 Pre Divider A pre divider before the phase comparator enables additional system clock resolution when the crystal oscillator frequency is 20 MHz The division factor is determined by the DIVF 0 4 bits in the PLPRCR 8 3 4 PLL Block Diagram As shown in Figure 8 3 the reference signal OSCCLK goes to the phase compara tor The phase comparator controls the direction up or down that the charge pump drives the voltage across the external filter capacitor XFC The direction depends on whether the feedback signal phase lags or leads the reference signal The output of the charge pump drives the VCO The output frequency of the VCO is divided down and fed back to the phase comparator for comparison with the reference signal OSCCLK The MF values zero to 4095 are mapped to multiplication factors of one to 4096 Note that when the PLL is operating in 1 1 mode refer to Table 8 1 the multi plication factor is one MF 0 The PLL output frequency is twice the maximum system frequency This double frequency is needed to generate GCLK1 and GCLK2 clocks On power up with a 4 MHz or 20 MHz crystal and the default MF settings VCOOUT will be 40 MHz and the system clock will be 20 MHz The equation for VCOOUT is shown below WooOUps OS sur
39. he same e g 12 5 ns 40 MHZ while the other become longer Note that MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 10 CLKOUT does not have a 5096 duty cycle when the general system clock is divided The CLKOUT waveform is the same as that of GCLK2 50 Divide by 1 LLULL Divide by 1 TTL LOLOL ELL Lr GCLK1 Divide by 2 GCLK2 Divide by 2 GCLK1 Divide by 4 GCLK Divide by 4 Figure 8 6 Divided System Clocks Timing Diagram The system clocks GCLK1 and GCLK2 frequency is FREQ FREQsysmax Sys 2PFNH or 2P NET where FREQsysmax VCOOUT 2 Therefore the complete equation for determining the system clock frequency is VCOOUT OSCCLK i MF 1 2 DIVF 1 2DFNH or 2DFNL 1 2 The clocks GCLK1 50 and GCLK2 50 freguency is FREQsysmax 1 2DFNH o oDFNL 1 EBDF 1 Figure 8 7 shows the timing of USIU clocks when DFNH 1 or DFNL 0 FREQs MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 11 GCLK1 GCLK2 GCLK1 50 EBDF 00 GCLK2 50 EBDF 00 CLKOUT EBDF 00 GCLK1 50 EBDF 01 GCLK2 50 EBDF 01 CLKOUT EBDF 01 Figure 8 7 Clocks Timing For DFNH 1 or DFNL 0 8 6 2 CLKOUT CLKOUT has the same frequency as the general system clock GCLK2 50 The CLK OUT frequency defaults to VCO 2 CLKOUT can drive f
40. m clock control register SCCR as shown in Figure 8 5 VCO 2 e g 40 MHz DENH Normal O DFNH Divider AN General System Clock DFNL DFNL Divider O Low Power Figure 8 5 General System Clocks Select The frequency of the general system clock can be changed on the fly by software The user may simply cause the general system clock to switch to its low frequency However in some applications there is a need for a high frequency during certain peri ods Interrupt routines for example may require more performance than the low frequency operation provides but must consume less power than in maximum fre quency operation The MPC555 provides a method to automatically switch between low and high frequency operation whenever one of the following conditions exists There is a pending interrupt from the interrupt controller This option is maskable by the PRQEN bit in the SCCR e The POW bit in the MSR is clear in normal operation This option is maskable by the PRQEN bit in the SCCR When neither of these conditions exists and the CSRC bit in PLPRCR is set the gen eral system clock switches automatically back to the low frequency Abrupt changes in the divide ratio can cause linear changes in the operating currents of the MPC555 Insure that the proper power supply filtering is available to handle this change instantaneously When the general system clock is divided its duty cycle is changed One phase remains t
41. me Description Disable backup clock for timers The DBCT bit controls the timers clock source while the chip is in limp mode If DBCT is set the timers clock tbclk rtclk source will not be the backup clock even if the system clock source is the backup clock ring oscillator The real time clock source will be EXTAL or EXTCLK according to RTSEL bit see description in bit 11 below and the time base clocks source will be determined according to TBS bit and MODCK1 0 If the chip is in limp mode the timer clock source is the backup limp clock 1 The timer clock source is either the external clock or the crystal depending on the current clock mode selected Clock output mode These bits control the output buffer strength of the CLKOUT and external bus pins These bits can be dynamically changed without generating spikes on the CLKOUT and external bus pins If CKLOUT is not connected to external circuits set both bits dis abling CLKOUT to minimize noise and power dissipation COM1 is determined by the hard 1 2 COM reset configuration word 00 Clock output enabled full strength output buffer bus pins full drive 01 Clock output enabled half strength output buffer bus pins reduced drive 10 Clock output disabled bus pins full drive 0 DBCT 11 Clock output disabled bus pins reduced drive MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 29 EI Table 8 9 SCC
42. ock It is also possible to switch to the backup clock by setting the STBUC bit If LME is cleared the option of using limp mode is disabled The loss of clock detector is not 15 LME active and any write to STBUC is ignored The LME bit is writable once by software after power on reset when the system clock is not backup clock BUCS 0 During power on reset the value of LME is determined by the MODCK 1 3 bits Refer to Table 8 1 0 Limp mode disabled 1 Limp mode enabled Enable engineering clock This field controls the output buffer strength of the ENGCLK pin When both bits are set the ENGCLK pin is held in the high state These bits can be dynam ically changed without generating spikes on the ENGCLK pin If ENGCLK is not connected to external circuits set both bits disabling ENGCLK to minimize noise and power dissipa 16 17 EECLK tion For measurement purposes the backup clock BUCLK can be driven externally on the ENGCLK pin 00 Engineering clock enabled full strength output buffer 01 Engineering clock enabled half strength output buffer 10 BUCLK is the output on the ENGCLK full strength output buffer 11 Engineering clock disabled Engineering clock division factor These bits define the freguency division factor between VCO 2 and ENGCLK Division factor can be from 1 ENGDIV 000000 to 64 ENGDIV 111111 These bits can be read and written at any time They are not affected by hard reset 18 23 E
43. one mode the wake up time may be up to 100 PLL input frequency clocks For a PLL input frequency of 4 MHz the wake up time is less than 125 us 8 8 3 4 Exiting from Power Down Mode Exit from power down mode is accomplished through hard reset External logic should assert HRESET in response to the TEXPS bit being set and TEXP pin being asserted The TEXPS bit is set by an enabled RTC PIT time base or decrementer interrupt The hard reset should be asserted for no longer than the time it takes for the power supply to wake up in addition to the PLL lock time When the TEXPS bit is cleared and the TEXP signal is negated assertion of hard reset sets the bit causes the pin to be asserted and causes an exit from power down low power mode Refer to 8 9 3 Keep Alive Power for more information 8 8 3 5 Low Power Modes Flow Figure 8 9 shows the flow among the different power modes MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 18 MSRpow Interrupt CSRC Software Normal Low LPM 00 CSRC 1 MSRpow Interrupt CSRC p io Software Doze Low LPM 01 CSRC 1 Interrupt A Software Sleep Mode 2 LPM 10 CSRC 0 Async Wake up Software Deep Sleep Mode RTC PIT TB DEC Interrupt LPM 11 0 Wake up 500 Input up npu TEXPS 1 Frequency Clocks Software Power Down Mode bro Interrupt follow
44. ting in limp mode BUCS 0 the RTSEL bit is 11 RTSEL ignored and the backup clock is the clock source for the RT and PIT clocks 0 OSCM clock is selected as input to RTC and PIT 1 EXTCLK clock is selected as the RTC and PIT clock source Backup clock status This status bit indicates the current system clock source When loss of clock is detected and the LME bit is set the clock source is the backup clock and this bit is set When the user sets the STBUC bit and LME bit is set the system switches to the backup kk BUCS clock and BUCS is set 0 System clock is not the backup clock 1 System clock is the backup clock MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 30 Table 8 9 SCCR Bit Settings Continued Bit s Name Description External bus division factor These bits define the frequency division factor between GCLK1 and GCLK2 and GCLK1 50 and GCLK2 50 CLKOUT is similar to GCLK2 50 The GCLK2 50 and GCKL1 50 are used by the external bus interface and memory controller in 13 14 EBDF order to interface to the external system The EBDF bits are initialized during hard reset using the hard reset configuration mechanism 00 CLKOUT is GCKL2 divided by 1 01 CLKOUT is GCKL2 divided by 2 1x Reserved Limp mode enable When LME is set the loss of clock monitor is enabled and any detection of loss of clock will switch the system clock automatically to backup cl
45. ull or half strength or be disabled The drive strength is controlled in the system clock and reset control register SCCR Disabling or decreasing the strength of CLKOUT can reduce power con sumption noise and electromagnetic interference on the printed circuit board When the PLL is acquiring lock the CLKOUT signal is disabled and remains in the low state provided that BUCS 0 8 6 3 Engineering Clock ENGCLK is an output clock with a 5096 duty cycle Its frequency defaults to VCO 4 ENGCLK frequency can be divided by a factor from one to 64 as controlled by the ENGDIV 0 5 bits in the SCCR ENGCLK can drive full or half strength or be disabled remaining in the high state The drive strength is controlled by the EECLK 0 1 bits in the SCCR Disabling ENGCLK can reduce power consumption noise and electro magnetic interference on the printed circuit board When the PLL is acquiring lock the ENGCLK signal is disabled and remains in the low state provided that BUCS 0 MPC555 CLOCKS AND POWER CONTROL MOTOROLA USER S MANUAL Revised 15 September 1999 8 12 NOTE Skew elimination between CLKOUT and ENGCLK is not guaranteed 8 7 Clock Source Switching For limp mode support clock source switching is supported If for any reason the clock source for the chip is not functioning the user has the option to switch the system clock to the backup clock ring oscillator BUCLK This circuit consists of a loss of clock detector
46. us interrupt The sources of the asynchro x1 nous interrupt are Asynchronous wake up interrupt from the interrupt controller RTC PIT or time base interrupts if enabled Decrementer exception The system response to asynchronous interrupts is fast The wake up time from nor mal low doze high doze low and sleep mode due to an asynchronous interrupt or decrementer exception is only three to four clock cycles of maximum system fre quency In 40 MHz systems this wake up requires 75 to 100 ns The asynchronous wake up interrupt from the interrupt controller is level sensitive one It will therefore be negated only after the reset of interrupt cause in the interrupt controller The timers RTC PIT time base or decrementer interrupts indication set status bits in the PLPRCR TMIST The clock module considers this interrupt to be pending asynchronous interrupt as long as the TMIST is set The TMIST status bit should be cleared before entering any low power mode Table 8 7 summarizes wake up operation for each of the low power modes Table 8 6 Power Mode Wake Up Operation Wake up Return Time from Wake up Operation Moda Method Event to Normal High Software Normal low gear Or Asynchronous interrupts Interrupt 3 4 maximum system cycles Synchronous interrupts Doze nign 3 4 actual system cycles Doze low Interrupt Sleep Interrupt 3 4 maximum system clocks 500 Oscillator Cycles Deep
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