F re e s c a le S e m ic o n d u c to r, I n c . ..
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1. MB3 1111111100 4 010101010101010101 0 MB4 00000011111 0 MB5 00000011101 1 010101010101010101 MB14 11111111000 1 101010101010101 0101 RX Global Mask EO 111111100000000001 11111111001 1 1010101010101010101 31 11111111001 0 22 RX Message In 11111111001 1 1010101010101010100 3 01111111000 0 ZA 01111111000 1 1010101010101010101 5 RX 14 Mask 01111111111 111111100000000000 10111111000 1 1010101010101010101 _6 RX Message In 01111111000 1 1010101010101010101 147 NOTES 1 Match for extended format MB3 2 Match for standard format MB2 3 No match for MB3 because of IDO 4 No match for MB2 because of ID28 5 No match for MB3 because of ID28 match for MB14 6 No match for MB14 because of 1D27 7 Match for MB14 13 4 3 Bit Timing The TouCAN module uses three 8 bit registers to set up the bit timing parameters required by the CAN protocol Control registers 1 and 2 CANCTRL1 CANCTRL2 contain the PROPSEG PSEG1 PSEG2 and the RJW fields which allow the user to configure the bit timing parameters The prescaler divide register PRESDIV allows the user to select the ratio used to derive the S clock from the system clock The time quanta clock operates at the S clock frequency Table 13 8 provides examples of sys MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More Inf ymathii Of rhis Product 13 8 Go to www freescale com Freescale Semiconductor Inc te2. NOTE In both the transmit and receive processes the first action in prepar ing a message buffer should be to deactivate the buffer by setting its code field to the proper value This requirement is mandatory to assure data coherency 13 5 3 Transmit Process The transmit process includes preparing a message buffer for transmission as well as the internal steps performed by the TouCAN to decide which message to transmit For the user this involves loading the message and ID to be transmitted into a message buffer and then activating that buffer as an active transmit buffer Once this is done the TouCAN will perform all additional steps necessary to transmit the message onto the CAN bus The user should prepare change a message buffer for transmission by executing the following steps Write the control status word to hold the transmit buffer inactive code 1000 Write the ID HIGH and ID LOW words Write the data bytes Write the control status word active TX code TX length eh NOTE Steps 1 and 4 are mandatory to ensure data coherency while prepar ing a message buffer for transmission Once an active transmit code is written to a transmit message buffer that buffer will begin participating in an internal arbitration process as soon as the CAN bus is sensed to be free by the receiver or at the inter frame space If there are multiple messages awaiting transmission this internal arbitration process selects the message
3. in bytes of the data to be transmitted located in offset 6 through D of the buffer This field TX Lenath is written by the CPU32 and is used as the DLC field value If RTR remote transmission request 9 1 the frame is a remote frame and will be transmitted without data field regardless of the value in TX length Data This field can store up to eight data bytes for a frame For RX frames the data is stored as it is re ceived from the bus For TX frames the CPU32 provides the data to be transmitted within the frame Reserved _ This word entry field 16 bits should not be accessed by the CPU32 MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL 13 4 For More Inf ymathii Of rhis Product Go to www freescale com Freescale Semiconductor Inc Table 13 2 Message Buffer Codes for Receive Buffers 0000 NOT ACTIVE message buffer is not active 0100 EMPTY message buffer is active and empty 0010 0010 FULL message buffer is full If a CPU32 read occurs be OVERRUN second frame was received into a full fore the new frame new re 0110 0110 P buffer before the CPU read the first one ceive code is 0010 An empty buffer was filled i o ji 0010 BUSY message buffer is now being filled with a new KY was 10 oxy receive frame This condition will be cleared within 20 A full overrun buffer was cycles 0110 filled Y was 1 NOTES 1 For TX mess
4. For More AE ae SR this Product 13 2 Go to www freescale com Freescale Semiconductor Inc NOTE The TouCAN has no hard wired protection against invalid bit field EI programming within its registers Specifically no protection is pro vided if the programming does not meet CAN protocol requirements Programming the TouCAN control registers is typically done during system initializa tion prior to the TouCAN becoming synchronized with the CAN bus The configuration registers can be changed after synchronization by halting the TouCAN module This is done when the user sets the HALT bit in the TouCAN module configuration register CANMCR The TouCAN responds by asserting the CANMCR NOTRDY bit Addition ally the control registers can be modified while the MCU is in background debug mode 13 4 TouCAN Architecture The TouCAN module utilizes a flexible design which allows each of its 16 message buffers to be assigned either as a transmit TX buffer or a receive RX buffer In addi tion to reduce the CPU32 overhead required for message handling each message buffer is assigned an interrupt flag bit to indicate successful completion of transmission or reception respectively 13 4 1 TX RX Message Buffer Structure Figure 13 3 displays the extended 29 bit ID message buffer structure Figure 13 4 displays the standard 11 bit ID message buffer structure 158 74 30 0 TIME STAMP CODE LENG
5. For more details on the message buffer locking mechanism and the effects on message buffer opera tion refer to 13 5 TouCAN Operation 13 4 2 Receive Mask Registers The receive mask registers are used as acceptance masks for received frame IDs The following masks are defined e A global mask used for receive buffers 0 13 e Two separate masks for buffers 14 and 15 The value of the mask registers should not be changed during normal operation If the mask register data is changed after the masked identifier of a received message is matched to a locked message buffer that message will be transferred into that mes sage buffer once it is unlocked regardless of whether that message s masked identifier still matches the receive buffer identifier Table 13 6 shows mask bit values MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More AE ae SR rhis Product 13 7 Go to www freescale com Freescale Semiconductor Inc Table 13 6 Receive Mask Register Bit Values El 0 The corresponding incoming ID bit is don t care 1 The corresponding ID bit is checked against the incoming ID bit to see if a match exists Table 13 7 shows mask examples for normal and extended messages Refer to APPENDIX D REGISTER SUMMARY for more information on RX mask registers Table 13 7 Mask Examples for Normal Extended Messages MB2 11111111000 0
6. as any reconfiguration which may be required during operation The following is a generic initialization sequence for the TouCAN A Initialize all operation modes 1 Initialize the transmit and receive pin modes in control register 0 CANCTRLO 2 Initialize the bit timing parameters PROPSEG PSEGS1 PSEG2 and RJW in control registers 1 and 2 CANCTRL 1 2 3 Select the S clock rate by programming the PRESDIV register 4 Select the internal arbitration mode LBUF bit in CANCTRL1 B Initialize message buffers 1 The control status word of all message buffers must be written either as an active or inactive message buffer 2 All other entries in each message buffer should be initialized as required C Initialize mask registers for acceptance mask as needed MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More AE ae SR this Product 13 11 Go to www freescale com Freescale Semiconductor Inc D Initialize TouCAN interrupt handler 1 Initialize the interrupt configuration register CANICR with a specific ni reguest level and vector base address 2 Initialize IARB 8 0 to a non zero value in CANMCR 3 Set the required mask bits in the IMASK register for all message buffer interrupts in CANCTRLO for bus off and error interrupts and in CANMCR for the WAKE interrupt E Negate the HALT bit in the module configuration register 1 At this point the TouCAN will attempt to synchronize with the CAN bus
7. buffer from which the next frame is transmitted When this process is over and a message buffer is selected for transmission the frame from that message buffer is transferred to the serial message buffer for transmission While transmitting the TouCAN will transmit no more than eight data bytes even if the transmit length contains a value greater than eight MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More AE ae SR this Product 13 12 Go to www freescale com Freescale Semiconductor Inc At the end of a successful transmission the value of the free running timer which was captured at the beginning of the identifier field on the CAN bus is written into the time stamp field in the message buffer The code field in the control status word of the mes sage buffer is updated and a status flag is set in the IFLAG register 13 5 3 1 Transmit Message Buffer Deactivation Any write access to the control status word of a transmit message buffer during the process of selecting a message buffer for transmission immediately deactivates that message buffer removing it from the transmission process While a message is being transferred from a transmit message buffer to a serial mes sage buffer if the user deactivates that transmit message buffer the message will not be transmitted If the user deactivates the transmit message buffer after the message is transferred to the serial message buffer the mes
8. register Refer to APPENDIX D REGISTER SUMMARY for more information on these registers Table 13 9 shows TouCAN interrupt priorities and their corresponding vector addresses MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More AE ae SR this Product 13 19 Go to www freescale com Freescale Semiconductor Inc Table 13 9 Interrupt Sources and Vector Addresses ja Buffer 0 XXX00000 Highest priority Buffer 1 XXX00001 Buffer 2 XXX00010 Buffer 3 XXX0001 1 Buffer 4 XXX00100 Buffer 5 XXX00101 Buffer 6 XXX00110 Buffer 7 XXX00111 Buffer 8 XXX01000 Buffer 9 XXX01001 Buffer 10 XXX01010 Buffer 11 XXX01011 Buffer 12 XXX01100 Buffer 13 XXX01101 Buffer 14 XXX01110 Buffer 15 XXX01111 Bus off XXX10000 Error XXX10001 Wake up XXX10010 Lowest priority MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More Informathti OA This Product 13 20 Go to www freescale com
9. the third bit of intermission to be recessive The TouCAN then waits for the completion of all internal activity except in the CAN bus interface to be com plete Afterwards the following events occur e The TouCAN shuts down its clocks stopping most internal circuits thus achieving maximum power savings e The bus interface unit continues to operate allowing the CPU32 to access the module configuration register e The TouCAN ignores its RX pins and drives its TX pins as recessive e The TouCAN loses synchronization with the CAN bus and the STOPACK and NOTRDY bits in the module configuration register are set To exit low power stop mode e Reset the TouCAN either by asserting one of the IMB reset lines or by asserting the SOFTRST bit CANMCR e Clear the STOP bit in CANMCR e The TouCAN module can optionally exit low power stop mode via the self wake mechanism If the SELFWAKE bit in CANMCR was set at the time the TouCAN entered stop mode then upon detection of a recessive to dominant transition on the CAN bus the TouCAN clears the STOP bit in CANMCR and its clocks begin running When in low power stop mode a recessive to dominant transition on the CAN bus causes the WAKEINT bit in the error and status register ESTAT to be set This event can generate an interrupt if the WAKEMSK bit in CANMCR is set Consider the following notes regarding low power stop mode e When the self wake mechanism activates the TouCAN tries to rece
10. Freescale Semiconductor Inc SECTION 13 CAN 2 0B CONTROLLER MODULE TouCAN This section is an overview of the TouCAN module Refer to D 10 TouCAN Module for information concerning TouCAN address map and register structure 13 1 General The TouCAN module is a communication controller that implements the controller area network CAN protocol an asynchronous communications protocol used in automotive and industrial control systems It is a high speed 1 Mbit sec short dis tance priority based protocol which can communicate using a variety of mediums for example fiber optic cable or an unshielded twisted pair of wires The TOuCAN sup ports both the standard and extended identifier ID message formats specified in the CAN protocol specification revision 2 0 part B The TouCAN module contains 16 message buffers which are used for transmit and receive functions It also contains message filters which are used to qualify the received message IDs when comparing them to the receive buffer identifiers Figure 13 1 shows a block diagram of the TouCAN CANTXO TRANSMITTER 16RX TX CANTX1 MESSAGE CONTROL CANRXO BUFFERS RECEIVER CANRX1 SLAVE BUS INTERFACE UNIT IMB THESE PINS ARE NOT BONDED ON THE MC68376 TOUCAN BLOCK Figure 13 1 TouCAN Block Diagram MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More AE ae SR this Pro
11. More Inis fm ARA WAThis Product 13 14 Go to www freescale com Freescale Semiconductor Inc mechanism will affect TouCAN operation ha 1 Reading a control status word of a message buffer triggers a lock for that 2 message buffer A new received message frame which matches the message buffer cannot be written into this message buffer while it is locked 2 To release a locked message buffer the CPU32 either locks another message buffer by reading its control status word or globally releases any locked message buffer by reading the free running timer 3 If a receive frame with a matching ID is received during the time the message buffer is locked the receive frame will not be immediately transferred into that message buffer but will remain in the serial message buffer There is no indi cation when this occurs 4 When a locked message buffer is released if a frame with a matching identifier exists within the serial message buffer then this frame will be transferred to the matching message buffer 5 If two or more receive frames with matching IDs are received while a message buffer with a matching ID is locked the last received frame with that ID is kept within the serial message buffer while all preceding ones are lost There is no indication when this occurs 6 If the user reads the control status word of a receive message buffer while a frame is being transferred from a serial message buffer the BUSY code will be indicate
12. TH CONTROL STATUS 2 ID 28 18 SRR IDE 1D 17 15 ID HIGH 4 ID 14 0 RTR ID LOW 6 DATA BYTE 0 DATA BYTE 1 8 DATA BYTE 2 DATA BYTE 3 A DATA BYTE 4 DATA BYTE5 C DATA BYTE 6 DATA BYTE 7 E RESERVED Figure 13 3 Extended ID Message Buffer Structure MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More AE ae SR this Product 13 3 Go to www freescale com Freescale Semiconductor Inc El 8 7 4 3 0 TIME STAMP CODE LENGTH CONTROL STATUS 2 ID 28 18 RTR 0 0 O ID_HIGH 4 16 BIT TIME STAMP ID LOW 6 DATA BYTE 0 DATA BYTE 1 8 DATA BYTE 2 DATA BYTE 3 A DATA BYTE 4 DATA BYTE 5 C DATA BYTE 6 DATA BYTE 7 E RESERVED Figure 13 4 Standard ID Message Buffer Structure 13 4 1 1 Common Fields for Extended and Standard Format Frames Table 13 1 describes the message buffer fields that are common to both extended and standard identifier format frames Table 13 1 Common Extended Standard Format Frames Time Stam Contains a copy of the high byte of the free running timer which is captured at the beginning of the ime stamP identifier field of the frame on the CAN bus Code Refer to Tables 13 2 and 13 3 RX Lenath Length in bytes of the RX data stored in offset 6 through D of the buffer This field is written by 9 the TouCAN module copied from the DLC data length code field of the received frame Length
13. age buffers upon read the BUSY bit should be ignored Table 13 3 Message Buffer Codes for Transmit Buffers X 1000 Message buffer not ready for transmit 0 1100 Data frame to be transmitted once unconditionally 1000 Remote frame to be transmitted once and message buffer be 1 1100 0100 comes an RK message buffer for data frames _ 0 1010 Data frame to be transmitted only as a response to a remote 1010 S frame always an Data frame to be transmitted only once unconditionally and g 0 1110 1010 then only as a response to remote frame always NOTES Q 1 When a matching remote request frame is detected the code for such a message buffer is changed to be m 1110 13 4 1 2 Fields for Extended Format Frames Table 13 4 describes the message buffer fields used only for extended identifier for mat frames MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More Inf mattun O8rhis Product 13 5 Go to www freescale com Freescale Semiconductor Inc Table 13 4 Extended Format Frames ID 28 18 17 15 Contains the 14 most significant bits of the extended identifier located in the ID HIGH word of the message buffer Substitute f A Remote Reduest Contains a fixed recessive bit used only in extended format Should be set to one by the user for GAR TX buffers It will be stored as received on the CAN bus for RX buffers ID Extended If extended for
14. d The user should wait until this code is cleared before continuing to read from the message buffer to ensure data coherency In this situation the read of the control status word will not lock the message buffer Polling the control status word of a receive message buffer can lock it preventing a message from being transferred into that buffer If the control status word of a receive message buffer is read it should then be followed by a read of the control status word of another buffer or by reading the free running timer to ensure that the locked buffer is unlocked 13 5 5 Remote Frames The remote frame is a message frame which is transmitted to request a data frame The TouCAN can be configured to transmit a data frame automatically in response to a remote frame or to transmit a remote frame and then wait for the responding data frame to be received When transmitting a remote frame the user initializes a message buffer as a transmit message buffer with the RTR bit set to one Once this remote frame is transmitted suc cessfully the transmit message buffer automatically becomes a receive message buffer with the same ID as the remote frame which was transmitted When a remote frame is received by the TouCAN the remote frame ID is compared to the IDs of all transmit message buffers programmed with a code of 1010 If there is an exact matching ID the data frame in that message buffer is transmitted If the RTR bit in the matching tra
15. duct 13 1 Go to www freescale com Freescale Semiconductor Inc 13 2 External Pins The TouCAN module interface to the CAN bus is composed of four pins CANTKO and CANTX1 which transmit serial data and CANRXO and CANRX1 which receive serial data Figure 13 2 shows a typical CAN system NOTE Pins CANTX1 and CANRX1 are not used on the MC68376 CAN STATION 1 CAN STATION 2 CAN STATION n CAN SYSTEM CAN CONTROLLER Joo fo eee TOUCAN CANTX0O CANTX1 CANRXO CANRX1 TRANSCEIVER Pee iE ee ee ia THESE PINS ARE NOT BONDED ON THE MC68376 CAN SYSTEM Figure 13 2 Typical CAN Network Each CAN station is connected physically to the CAN bus through a transceiver The transceiver provides the transmit drive waveshaping and receive compare functions required for communicating on the CAN bus It can also provide protection against damage to the TouCAN caused by a defective CAN bus or a defective CAN station 13 3 Programmer s Model The TouCAN module address space is split into 128 bytes starting at the base address and then an extra 256 bytes starting at the base address 128 The upper 256 are fully used for the message buffer structures Out of the lower 128 bytes only part is occupied by various registers Refer to D 10 TouCAN Module for detailed information on the TouCAN address map and register structure MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL
16. ed one If a match is detected the following actions occur MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More AE ae SR this Product 13 13 Go to www freescale com Freescale Semiconductor Inc 1 The frame is transferred to the first lowest entry matching receive message buffer E 2 The value of the free running timer captured at the beginning of the identifier field on the CAN bus is written into the time stamp field in the message buffer The ID field data field and RX length field are stored 3 4 The code field is updated 5 The status flag is set in the IFLAG register The user should read a received frame from its message buffer in the following order 1 Control status word mandatory as it activates the internal lock for this buffer 2 ID optional since it is needed only if a mask was used 3 Data field word s 4 Free running timer optional as it releases the internal lock If a read of the free running timer is not performed that message buffer remains locked until the read process starts for another message buffer Only a single message buffer is locked at a time When reading a received message the only mandatory read oper ation is that of the control status word This assures data coherency If the BUSY bit is set in the message buffer code the CPU32 should defer accessing that buffer until this bit is negated Refer to Table 13 2 NOTE The CPU32 should check the
17. ess e No transfer of RX TX frames to and from a serial message buffer and no TX frame awaiting transmission in any message buffer e No CPU32 access to the TouCAN module e The TouCAN is not in debug mode low power stop mode or the bus off state While its clocks are stopped if the TouCAN senses that any one of the aforementioned conditions is no longer true it restarts its clocks The TouCAN then continues to mon itor these conditions and stops restarts its clocks accordingly 13 7 Interrupts The TouCAN is capable of generating one interrupt level on the IMB This level is programmed into the priority level bits in the interrupt configuration register CANICR This value determines which interrupt signal is driven onto the bus when an interrupt is requested When an interrupt is requested the CPU32 initiates an IACK cycle The TouCAN decodes the IACK cycle and compares the CPU32 recognized level to the level that it MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More KU AE ae SR this Product 13 18 Go to www freescale com Freescale Semiconductor Inc is currently requesting If a match occurs then arbitration begins If the TouCAN wins arbitration it generates a uniquely encoded interrupt vector that indicates which event ni is reguesting service This encoding scheme is as follows e The higher order bits of the interrupt vector come from the IVBA 2 0 field in CANICR e The low orde
18. he TouCAN transmits a value and receives a matching response a successful bit transmission is indicated 13 4 1 4 Serial Message Buffers To allow double buffering of messages the TouCAN has two shadow buffers called serial message buffers These two buffers are used by the TouCAN for buffering both received messages and messages to be transmitted Only one serial message buffer is active at a time and its function depends upon the operation of the TouCAN at that time At no time does the user have access to or visibility of these two buffers 13 4 1 5 Message Buffer Activation Deactivation Mechanism Each message buffer must be activated once it is configured for the desired operation by the user A buffer is activated by writing the appropriate code to the control status word for that buffer Once the buffer is activated it will begin participating in the normal transmit and receive processes MC68336 376 USER S MANUAL CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA For More Inim atn WM rhis Product 13 6 Go to www freescale com Freescale Semiconductor Inc Likewise a buffer is deactivated by writing the appropriate deactivation code to the control status word for that buffer Deactivation of a buffer is typically done when the ni user desires to reconfigure the buffer for example to change the buffer s function RX to TX or TX to RX Deactivation should also be done before changing a receive buffer s me
19. hen the STOP bit is set the TouCAN will assume that debug mode should be exited As a result it will try to synchronize with the CAN bus and only then will it await the conditions required for entry into low power stop mode e Unlike other modules the TouCAN does not come out of reset in low power stop mode The basic TouCAN initialization procedure see 13 5 2 TouCAN Initial ization should be executed before placing the module in low power stop mode e If the TOUCAN is in low power stop mode with the self wake mechanism engaged and is operating with a single system clock per time quantum there can be ex treme cases in which TouCAN wake up on recessive to dominant edge may not conform to the CAN protocol TouCAN synchronization will be shifted one time quantum from the wake up event This shift lasts until the next recessive to dom inant edge which resynchronizes the TouCAN to be in conformance with the CAN protocol The same holds true when the TouCAN is in auto power save mode and awakens on a recessive to dominant edge 13 6 3 Auto Power Save Mode Auto power save mode enables normal operation with optimized power savings Once the auto power save APS bit in CANMCR is set the TouCAN looks for a set of con ditions in which there is no need for the clocks to be running If these conditions are met the TouCAN stops its clocks thus saving power The following conditions will activate auto power save mode e No RX TX frame in progr
20. itrate against the message which transmit ted the early SOF e The TouCAN bit time must be programmed to be greater than or equal to nine system clocks or correct operation is not guaranteed 13 4 4 Error Counters The TouCAN has two error counters the transmit TX error counter and the receive RX error counter Refer to APPENDIX D REGISTER SUMMARY for more informa tion on error counters The rules for increasing and decreasing these counters are described in the CAN protocol and are fully implemented in the TouCAN Each counter has the following features e 8 bit up down counter e Increment by 8 RX error counter also increments by one e Decrement by one e Avoid decrement when equal to zero e RX error counter reset to a value between 119 and 127 inclusive when the MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More Inf ymathti Of rhis Product 13 9 Go to www freescale com Freescale Semiconductor Inc TouCAN transitions from error passive to error active e Following reset both counters reset to zero e Detect values for error passive bus off and error active transitions e Cascade usage of TX error counter with an additional internal counter to detect the 128 occurrences of 11 consecutive recessive bits necessary to transition from bus off into error active Both counters are read only except in test freeze halt modes The TouCAN responds to any bus state as described in the CAN prot
21. ive the frame that woke it up It assumes that the dominant bit detected is a start of frame bit It will not arbitrate for the CAN bus at this time e If the STOP bit is set while the TouCAN is in the bus off state then the TouCAN will enter low power stop mode and stop counting recessive bit times The count will continue when STOP is cleared e To place the TouCAN in low power stop mode with the self wake mechanism engaged write to CANMCR with both STOP and SELFWAKE set then wait for the TouCAN to set the STOPACK bit e To take the TouCAN out of low power stop mode when the self wake mechanism is enabled write to CANMCR with both STOP and SELFWAKE clear then wait for the TouCAN to clear the STOPACK bit e The SELFWAKE bit should not be set after the TouCAN has already entered low power stop mode MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More AE ae SR this Product 13 17 Go to www freescale com Freescale Semiconductor Inc If both STOP and SELFWAKE are set and a recessive to dominant edge immediately occurs on the CAN bus the TouCAN may never set the STOPACK bit and the STOP bit will be cleared e To prevent old frames from being sent when the TouCAN awakes from low power stop mode via the self wake mechanism disable all transmit sources including transmit buffers configured for remote request responses before placing the TOouCAN in low power stop mode e If the TouCAN is in debug mode w
22. m clock CAN bit rate and S clock bit timing parameters Refer to APPENDIK D REGISTER SUMMARY for more information on the bit timing registers EN Table 13 8 Example System Clock CAN Bit Rate and S Clock Frequencies 25 1 25 25 1 20 1 10 20 10 20 2 1 16 1 8 16 8 16 2 1 25 0 125 1 1 25 2 5 8 10 20 25 20 10 20 0 125 1 2 2 5 8 16 20 20 10 8 16 0 125 1 2 8 16 16 8 13 4 3 1 Configuring the TouCAN Bit Timing The following considerations must be observed when programming bit timing functions e f the programmed PRESDIV value results in a single system clock per one time quantum then the PSEG2 field in CANCTRL2 register should not be pro grammed to zero e f the programmed PRESDIV value results in a single system clock per one time quantum then the information processing time IPT equals three time quanta otherwise it equals two time quanta If PSEG2 equals two then the TouCAN transmits one time quantum late relative to the scheduled sync segment e If the prescaler and bit timing control fields are programmed to values that result in fewer than ten system clock periods per CAN bit time and the CAN bus loading is 100 anytime the rising edge of a start of frame SOF symbol transmitted by another node occurs during the third bit of the intermission between messages the TouCAN may not be able to prepare a message buffer for transmission in time to begin its own transmission and arb
23. mat frame is used this field should be set to one If zero standard format frame IDE should be used ID 14 0 Bits 14 0 of the extended identifier located in the ID LOW word of the message buffer Remote This bitis located in the least significant bit of the ID LOW word of the message buffer Transmission 0 Data Frame 1 Remote Frame Request RTR 13 4 1 3 Fields for Standard Format Frames Table 13 5 describes the message buffer fields used only for standard identifier format frames Table 13 5 Standard Format Frames 16 Bit Time Stamp The ID LOW word which is not needed for standard format is used in a standard format buffer to store the 16 bit value of the free running timer which is captured at the beginning of the iden tifier field of the frame on the CAN bus ID 28 18 Contains bits 28 18 of the identifier located in the ID HIGH word of the message buffer The four least significant bits in this register corresponding to the IDE bit and ID 17 15 for an extended identifier message must all be written as logic zeros to ensure proper operation of the TouCAN RTR This bit is located in the ID HIGH word of the message buffer 0 data frame 1 remote frame RTR SRR Bit Treatment If the TouCAN transmits this bit as a one and receives it as a zero an arbitration loss is indicat ed If the TouCAN transmits this bit as a zero and is receives it as a one a bit error is indicated If t
24. ng transmitted the time stamp entry will be written into the transmit message buffer once the transmission has completed successfully The free running timer can optionally be reset upon the reception of a frame into mes sage buffer 0 This feature allows network time synchronization to be performed 13 5 TouCAN Operation The basic operation of the TouCAN can be divided into three areas e Reset and initialization of the module e Transmit message handling e Receive message handling Example sequences for performing each of these processes is given in the following paragraphs 13 5 1 TouCAN Reset The TouCAN can be reset in two ways e Hard reset using one of the IMB reset lines e Soft reset using the SOFTRST bit in the module configuration register Following the negation of reset the TouCAN is not synchronized with the CAN bus and the HALT FRZ and FRZACK bits in the module configuration register are set In this state the TouCAN does not initiate frame transmissions or receive any frames from the CAN bus The contents of the message buffers are not changed following reset Any configuration change initialization requires that the TouCAN be frozen by either asserting the HALT bit in the module configuration register or by reset 13 5 2 TouCAN Initialization Initialization of the TouCAN includes the initial configuration of the message buffers and configuration of the CAN communication parameters following a reset as well
25. nsmit message buffer is set the TouCAN will transmit a remote frame as a response MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More AE ae SR rhis Product 13 15 Go to www freescale com Freescale Semiconductor Inc A received remote frame is not stored in a receive message buffer It is only used to trigger the automatic transmission of a frame in response The mask registers are not used in remote frame ID matching All ID bits except RTR of the incoming received frame must match for the remote frame to trigger a response transmission 13 5 6 Overload Frames Overload frame transmissions are not initiated by the TouCAN unless certain condi tions are detected on the CAN bus These conditions include e Detection of a dominant bit in the first or second bit of intermission e Detection of a dominant bit in the seventh last bit of the end of frame EOF field in receive frames e Detection of a dominant bit in the eighth last bit of the error frame delimiter or overload frame delimiter 13 6 Special Operating Modes The TouCAN module has three special operating modes e Debug mode e Low power stop mode e Auto power save mode 13 6 1 Debug Mode Debug mode is entered by setting the HALT bit in the CANMCR or by assertion of the IMB FREEZE line In both cases the FRZ1 bit in CANMCR must also be set to allow HALT or FREEZE to place the TouCAN in debug mode Once entry into debug mode is reque
26. ocol transmitting an error active or error passive flag delaying its transmission start time error passive and avoiding any influence on the bus when in the bus off state The following are the basic rules for TouCAN bus state transitions e f the value of the TX error counter or RX error counter increments to a value greater than or equal to 128 the fault confinement state FCS 1 0 field in the error status register is updated to reflect an error passive state e lf the TouCAN is in an error passive state and either the TX error counter or RX error counter decrements to a value less than or equal to 127 while the other er ror counter already satisfies this condition the FCS 1 0 field in the error status register is updated to reflect an error active state e f the value of the TX error counter increases to a value greater than 255 the FCS 1 0 field in the error status register is updated to reflect a bus off state and an interrupt may be issued The value of the TX error counter is reset to zero e If the TouCAN is in the bus off state the TX error counter and an additional inter nal counter are cascaded to count 128 occurrences of 11 consecutive recessive bits on the bus To do this the TX error counter is first reset to zero then the in ternal counter begins counting consecutive recessive bits Each time the internal counter counts 11 consecutive recessive bits the TX error counter is incremented by one and the internal counte
27. r five bits are an encoded value that indicate which of the 19 TouCAN interrupt sources is requesting service Figure 13 5 shows a block diagram of the interrupt hardware INTERRUPT REQUEST gt LEVEL INTERRUPT ILCAN 2 0 LEVEL E IRQ 7 1 DECODER MASKS BUFFER 16 INTERRUPT z INTERRUPTS 19 PRIORITY gt ENCODER MODULE INTERRUPT INTERRUPT BUS OFF gt ENABLE ee LOGIC ERROR gt 3 WAKE UP gt VECTOR BASE ADDRESS IVBA 2 0 TOUCAN INTERRUPT GEN Figure 13 5 TouCAN Interrupt Vector Generation Each one of the 16 message buffers can be an interrupt source if its corresponding IMASK bit is set There is no distinction between transmit and receive interrupts for a particular buffer Each of the buffers is assigned a bit in the IFLAG register An IFLAG bit is set when the corresponding buffer completes a successful transmission recep tion An IFLAG bit is cleared when the CPU32 reads IFLAG while the associated bit is set and then writes it back as zero and no new event of the same type occurs between the read and the write actions The other three interrupt sources bus off error and wake up act in the same way and have flag bits located in the error and status register ESTAT The bus off and error interrupt mask bits BOFFMSK and ERRMSk are located in CANCTRLO and the wake up interrupt mask bit WAKEMSk is located in the module configuration
28. r is reset to zero When the TX error counter reach es the value of 128 the FCS 1 0 field in the error status register is updated to be error active and both error counters are reset to zero Any time a dominant bit is detected following a stream of less than 11 consecutive recessive bits the inter nal counter resets itself to zero but does not affect the TX error counter value e If only one node is operating in a system the TX error counter will increment with each message it attempts to transmit due to the resulting acknowledgment er rors However acknowledgment errors will never cause the TouCAN to transition from the error passive state to the bus off state e If the RX error counter increments to a value greater than 127 it will stop incre menting even if more errors are detected while being a receiver After the next successful message reception the counter is reset to a value between 119 and 127 to enable a return to the error active state 13 4 5 Time Stamp The value of the free running 16 bit timer is sampled at the beginning of the identifier field on the CAN bus For a message being received the time stamp will be stored in the time stamp entry of the receive message buffer at the time the message is written MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More AE ae SR rhis Product 13 10 Go to www freescale com gl Freescale Semiconductor Inc into that buffer For a message bei
29. sage will be transmitted but no interrupt will be requested and the transmit code will not be updated If a message buffer containing the lowest ID is deactivated while that message is undergoing the internal arbitration process to determine which message should be sent then that message may not be transmitted 13 5 3 2 Reception of Transmitted Frames The TouCAN will receive a frame it has transmitted if an empty message buffer with a matching identifier exists 13 5 4 Receive Process The receive process includes configuring message buffers for reception the transfer of received messages by the TouCAN from the serial message buffers to the receive message buffers with matching IDs and the retrieval of these messages by the user The user should prepare change a message buffer for frame reception by executing the following steps 1 Write the control status word to hold the receive buffer inactive code 0000 2 Write the ID HIGH and ID LOW words 3 Write the control status word to mark the receive message buffer as active and empty NOTE Steps 1 and 3 are mandatory for data coherency while preparing a message buffer for reception Once these steps are performed the message buffer functions as an active receive buffer and participates in the internal matching process which takes place every time the TouCAN receives an error free frame In this process all active receive buffers compare their ID value to the newly receiv
30. ssage identifier or before loading a new message to be transmitted into a transmit buffer For more details on activation and deactivation of message buffers and the effects on message buffer operation refer to 13 5 TouCAN Operation 13 4 1 6 Message Buffer Lock Release Busy Mechanism In addition to the activation deactivation mechanism the TouCAN also utilizes a lock release busy mechanism to assure data coherency during the receive process The mechanism includes a lock status for each message buffer and utilizes the two serial message buffers to facilitate frame transfers within the TouCAN Reading the control status word of a receive message buffer triggers the lock for that buffer While locked a received message cannot be transferred into that buffer from one of the SMBs If a message transfer between the message buffer and a serial message buffer is in progress when the control status word is read the BUSY status will be indicated in the code field and the lock will not be activated The user can release the lock on a message buffer in one of two ways Reading the control status word of another message buffer will lock that buffer releasing the pre viously locked buffer A global release can also be performed on any locked message buffer by reading the free running timer Once a lock is released any message transfers between an SMB and a message buff er which was delayed due to that buffer being locked will take place
31. status of a message buffer by reading the status flag in the IFLAG register and not by reading the control status word code field for that message buffer This prevents the buffer from being locked inadvertently Because the received identifier field is always stored in the matching receive message buffer the contents of the identifier field in a receive message buffer may change if one or more of the ID bits are masked 13 5 4 1 Receive Message Buffer Deactivation Any write access to the control status word of a receive message buffer during the pro cess of selecting a message buffer for reception immediately deactivates that message buffer removing it from the reception process If a receive message buffer is deactivated while a message is being transferred into it the transfer is halted and no interrupt is requested If this occurs that receive message buffer may contain mixed data from two different frames Data should never be written into a receive message buffer If this is done while a mes sage is being transferred from a serial message buffer the control status word will reflect a full or overrun condition but no interrupt will be requested 13 5 4 2 Locking and Releasing Message Buffers The lock release busy mechanism is designed to guarantee data coherency during the receive process The following examples demonstrate how the lock release busy MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For
32. sted the TouCAN waits until an intermission or idle condition exists on the CAN bus or until the TouCAN enters the error passive or bus off state Once one of these conditions exists the TouCAN waits for the comple tion of all internal activity When this happens the following events occur e The TouCAN stops transmitting receiving frames e The prescaler is disabled thus halting all CAN bus communication e The TouCAN ignores its RX pins and drives its TX pins as recessive e The TouCAN loses synchronization with the CAN bus and the NOTRDY and FRZACK bits in CANMCR are set e The CPU32 is allowed to read and write the error counter registers After engaging one of the mechanisms to place the TouCAN in debug mode the user must wait for the FRZACK bit to be set before accessing any other registers in the TouCAN otherwise unpredictable operation may occur To exit debug mode the IMB FREEZE line must be negated or the HALT bit in CANMCR must be cleared MC68336 376 CAN 2 0B CONTROLLER MODULE TouCAN MOTOROLA USER S MANUAL For More AE ae SR this Product 13 16 Go to www freescale com Freescale Semiconductor Inc Once debug mode is exited the TouCAN will resynchronize with the CAN bus by wait ing for 11 consecutive recessive bits before beginning to participate in CAN bus communication 13 6 2 Low Power Stop Mode Before entering low power stop mode the TouCAN will wait for the CAN bus to be in an idle state or for
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