addressing up to 4 mbytes of memory from a st9+ with a 16
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1. ROMLESS or almost 4 Mbytes with an OTP EPROM FLASH device This last solution uses the P2 I O port to output the 22 bit address 2 ACCESSING UP TO 64 KBYTES OF EXTERNAL MEMORY WITHOUT SOFTWARE OVERHEAD The ST9 outputs a 16 bit address multiplexed with the 8 bit data So to access 64 Kbytes of memory we only need to make the correct hardware connections between the memory de vices and the microcontroller These connections are described in Figure 2 Figure 2 Accessing 64 Kbytes of external memory EXTERNAL MEMORY 64 K 74HC573 Sige 16 bit address OTP ROM ROMLESS FLASH 8 bit data ROM M27C1001 RAM M48Z64Y Flash M29F010b R W RAM and Flash only E The R W signal is only needed for RAM and Flash or mixed memory components The pull up resistor is needed only when using ROMLESS devices Examples of memory mapping are given in Figure 3 and Figure 4 4 2 14 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY Figure 3 Memory mapping for 64K of external memory with ST90158 OTP Reserved ee 1K cae 64K External Memory 64K Internal ROM Figure 4 Memory mapping for 64 K of external memory with ST90R158 ROMLESS 1K RAM Unused 64K External Memory 3 14 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY 3 ACCESSING UP TO 2 OR 4 MBYTES WITH ANY ST9 3 1 PRINCIPLE As previously mentioned in Section 1 the ST9 handles 22 bit addresses internally but outputs only the 16 LSBs of the a2. 14 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY 3 4 4 Emulation For emulation during the down load of the application into the emulator the access to the dy namic segments cannot be configured properly since the emulator is in reset state To get around this we can use the internal memory of the emulator as a buffer and then transfer the information from the emulator memory declared as SYSTEM memory in the Mapfile of ST Visual Debugger STVD9 to the external memory declared as USER memory in the Map file of STVD9 This operation is done in the Start up file of the software example after the initiali zation of the external memory interface if needed It is done by the secinfo table Refer to GCC9 user manual for more information on the secinfo section By using this process we need twice as much memory since any external memory needs to have a buffer Therefore the maximum amount of memory available during emulation is 2MB 3 4 5 Capabilities and limitations Due to the fact that dynamic segments can only be accessed one by one some limitations apply to the way you write your program and manipulate data Table 1 summarizes the capa bilities and limitations Table 1 Software capabilities and limitations Type ot data J Location J Capabity_ Emulation Code OK Jump or call from DS to another DS Jump or call from DS to the same DS es O Located in the SS and used by a program Yes in the SS or DS es s OK A
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4. ddress through the external memory interface In this section we will see how by handling it in software it is possible to access almost 2M with a ROMLESS device or almost to 4M bytes with an OTP ROM or Flash device To access more than 64K of external memory you need to output the 6 Most Significant Bits MSBs of the address To do this we have chosen to use the 6 LSBs of Port 2 refer to Figure 53 Port 2 will be used by software to select the Dynamic Segment you want to access External memory segments and Internal memory segments are two different addressable areas For simplicity both types of segment are numbered in the same way Figure 5 ST9 Schematic 8 bit data bus ST9 internal memory 22 bit address 16 bit address multiplexed with 8 bit data bus External Memory PO 0 7 Interface P4 0 7 AS R W DS DS2 ST92F120 only I O port logic P2 0 5 4 14 4 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY Figure 6 Static and Dynamic Segments Dynamic segments External memory Static Segments Internal or External memory 3 2 DEFINITION STATIC SEGMENT SS A segment of memory which can always be accessed whatever the value of the Dynamic Segment selected value of Port 2 data register P2DR In an OTP ROM FLASH microcontroller the internal memory can always be accessed and therefore is contained in static segments For example in the ST90158 Segment 0 ROM and Seg 20 RAM are static se
5. ents and the Dynamic segments In this example A15 is used to select either Static or Dynamic segments As a consequence of this the Static and Dynamic Segments are 32K bytes in size so we can access only 32k of external memory in each segment If you compare the address of the external memory described in Figure 9 and the address of the ST9 described in Figure 10 you can see the difference starts from the 16th bit of the address Like in ST90158 OTP devices Segments 20 21 22 of external memory cannot be accessed The total accessible memory is 2M 64 Kbytes x 64 segments 3 x 32K internal segment 32K static page 1K internal RAM 1920K bytes Figure 10 shows the memory map with segments containing 32K of memory 8 14 4 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY Figure 9 Accessing almost 2M with the ST90R158 74HC573 EXTERNAL MEMORY ST90R158 32 Kbytes POf0 7 z E P1 0 7 15 bit address 8 bit data EXTERNAL MEMORY A 0 14 Siibyiss 74HC04 P2 0 7 21 bit address E R W RAM and Flash only 0x01 8000 8 bit data 0x01 0000 G 0x00 8000 0x00 0000 It is possible to increase the amount of accessible memory by reducing the size of the static would increase the complexity of the hardware and software 9 14 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY Figure 10 Memory mapping for accessing 2M of external memory with ST90R158 External Memory 32K Seg 3F 32K Ext
6. er Dynamic Segment The number of instructions and cycles generated by this macro depends on the location of the P2DR register it can go from 3 bytes 6 cycles to 5 bytes 10 cycles Depending on the DPRREM bit in the EMR2 Register the P2DR register can be located in group E of the Reg ister File RF or in group F page 21 of the RF Read the datasheet and C compiler manual carefully since the programming model has an impact on the DPRREM register 3 4 2 Direct Memory Access DMA The following paragraph is about DMA transfer between a peripheral and memory There are no restrictions on DMA transfer between a peripheral and the Register File In most applications the DMA can occur at any moment during program execution Data to be transferred needs to be located in the Static Segment Nevertheless if it is really needed we can put the data in the Dynamic Segment But during DMA we can only run code in the Static Segments or in the same Static Segment as the one where the data is located 3 4 3 INTERRUPTS Interrupts can occur at any time during code execution Therefore interrupt vectors and rou tines should be located in the Static Segment in order to be accessible at any time Nevertheless a routine from a Dynamic Segment can be called by the interrupt routine In this case refer to the datasheet to be sure you have configured your microcontroller to save the CSR refer to the description of the ENCSR bit in the EMR2 register 11
7. ernal Memory 7 RAM 32K External Not Available 32K External Memory 0x02 8000 0x02 0000 E Dynamic segment 32K External Memory 0x01 8000 0x01 0000 static segment 32K External Memory 0x00 8000 32K External Memory 0x00 0000 10 14 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY 3 4 SOFTWARE IMPLEMENTATION 3 4 1 Calling functions or manipulating data in a dynamic segment Before calling a function or manipulating data ina Dynamic Segment we need to write the cor rect value in the Port 2 data register P2DR to select the segment This can be done automat ically using a macro called set_seg which is in the extmem h file This macro uses the function name or the data address as a parameter set_seg my_function_name set_seg amp data_name This macro must be used each time we want to call a function or manipulate data which is in a dynamic Segment other than the current one It is not necessary to use this macro to call a function in the same dynamic segment as the caller function or to manipulate data in the same dynamic Nevertheless for data manipulation is advised to set the segment using the macro for code portability Once this macro is implemented in your code if you change the location of your code to another Dynamic Segment the segment number is computed automatically Nevertheless make sure you change the associated data segment too since code cannot ac cess data located in anoth
8. gments The size of the memory in a segment can be from zero to 64K The number of static segments and the amount of memory in each segment depends on the microcontroller In the case of ROMLESS devices the static segment must be a special area of external memory which is not connected to Port 2 and is therefore not dynamic At least one static segment is needed in any application DYNAMIC SEGMENT DS A segment of the external memory which is accessible only if it has been selected by the user Its access depends on the P2DR Port 2 data register value The size of a dynamic segment can be from 0 to 64K 5 14 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY 3 3 HARDWARE IMPLEMENTATION 3 3 1 Example using a microcontroller with internal memory In this example using the ST90158 with 64K of internal ROM the microcontroller s internal memory can be used as a Static Segment The hardware connections are shown in Figure 7 Figure 7 Accessing almost 4M with the ST90158 74HC573 EXTERNAL MEMORY 4Mbytes A 8 15 A 0 21 P1 0 7 22 bit address ST90158 PO O 7 8 bit data P2 0 7 74HC04 R W RAM and Flash only G Seg 0 Not Sei Due to the fact we are using OTP or ROM devices when the user accesses an address in the internal segment no external signals AS DS will be output by the ST9 if the ETO bit in the EMR1 register is correctly configured please refer to the datasheet This is the ca
9. lways seen Constant Located in the DS and used by a program Yes Not seen if the DS is in the SS or the same DS as the constant not selected Located in the DS and used by a program No N A in another DS Yes No Always seen Not seen if the DS is not selected Always seen in the SS or DS in the SS or the same DS as the constant Located in the DS and used by a program in the SS or DS Un initialized varia Located in the DS and used by a program Not seen if the DS is Located in the DS and used by a program po No O N A in another DS Legend SS Static Segment DS Dynamic Segment 4 12 14 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY 3 5 SOFTWARE EXAMPLE A software example using the ST9 demonstration board and the ST90158EMU2B is available You will find in it examples all the possible code manipulations call and use of data con stants initialized variables You will be able to observe the transfer process for the emula tion capability The example downloads the program into the external RAM of the demonstra tion board 13 14 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY THE PRESENT NOTE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS WITH INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE TIME AS A RESULT STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY DIRECT INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING FROM THE CONTENT OF SUCH A NOTE AND O
10. ren AN1069 Sf APPLICATION NOTE ADDRESSING UP TO 4 MBYTES OF MEMORY FROM A ST9 WITH A 16 BIT EXTERNAL BUS By Microcontroller Division Applications INTRODUCTION This application note is to help developers of ST9 applications that need to address external memory It refers to ST9 microcontrollers which have only a 16 bit external address bus such as the ST90158 The information in this application note does not apply to ST9 micro controllers that have a 22 bit external address bus 1 ST9 EXTERNAL MEMORY MANAGEMENT Through the Memory Management Unit MMU ST9 devices can internally address up to 4M bytes of linear memory using a 22 bit address bus refer to the datasheet or ST9 user guide for more information on the MMU Nevertheless most general purpose ST9 microcontrollers do not output this 22 bit address bus they only output the 16 Least Significant Bits LSBs of the 22 bit address This 16 bit ad dress is output on two 8 bit ports PO and P1 This allows the user to address 64 Kbytes 218 of external memory directly Figure 1 ST9 Memory Access Overview 8 BIT DATA 22 BIT ADDRESS AN1069 0700 1 14 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY In the first part of this application note we will see how to use the existing interface to address 64 Kbytes or 128 Kbytes ST92F 120 only of external memory without any additional software overhead In the second part we will see how to address almost 2 Mbytes with a
11. se for seg ments 0 21 22 and 23h in the ST90158 Therefore any external memory that uses the same segment number as the internal memory will not be accessible To make it accessible we would need a dedicated logical unit 6 14 4 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY Using the ST90158 the maximum accessible memory will be 4M total accessible memory 4x 64 k internal segments 1K internal RAM 64K internal ROM 3905K bytes The size of each dynamic segment is 64 Kbytes in this case We can represent the memory seen by the microcontroller as shown in Figure 8 Note When using ST92F 120 it is not possible to access any external segments other than segments 2 and 3 So the maximum amount of external memory that can be accessed by the ST92F120 is 128 Kbytes Figure 8 Memory map for accessing 4M of external memory with the ST90158 Seg 3F 64K External Memory 64K External Memory 1K RAM 64K External Memory 64K External Memory I Dynamic segment 64K Internal ROM za Static segment SZA 7 14 ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY 3 3 2 Example Using a ROMless microcontroller If we use a ROMLESS ST90158 device which has no internal ROM we cannot use internal memory as a Static Segment therefore we have to create an external Static Segment An ex ample of the hardware implementation is given in Figure 9 The external memory capability is divided into 2 parts the Static segm
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