CY7C601xx, CY7C602xx
Two important variables used for all functions are KEY1 and KEY2. These variables help discriminate between valid and inadvertent SSCs. KEY1 always has a value of 3Ah, while KEY2 has the same value as the stack pointer when the SROM function begins execution. This is the Stack Pointer value when the SSC opcode is executed, plus three. If either of the keys do not match the expected values, the M8C halts (with the exception of the SWBootReset function). The following code puts the correct value in KEY1 and KEY2. The code starts with a halt, to force the program to jump directly into the setup code and not run into it.
halt
SSCOP: mov [KEY1], 3ah mov X, SP
mov A, X add A, 3
mov [KEY2], A
Table 11-2. SROM Function Parameters
Variable Name | SRAM Address |
Key1/Counter/Return Code | 0,F8h |
|
|
Key2/TMP | 0,F9h |
|
|
BlockID | 0,FAh |
|
|
Pointer | 0,FBh |
|
|
Clock | 0,FCh |
|
|
Mode | 0,FDh |
|
|
Delay | 0,FEh |
|
|
PCL | 0,FFh |
|
|
11.4.1 Return Codes
The SROM also features Return Codes and Lockouts.
Return codes determine the success or failure of a particular function. The return code is stored in KEY1’s position in the parameter block. The CheckSum and TableRead functions do not have return codes because KEY1’s position in the parameter block is used to return other data.
Table 11-3. SROM Return Codes
Return Code | Description |
00h | Success |
|
|
01h | Function not allowed due to level of protection |
| on block |
02h | Software reset without hardware reset |
|
|
03h | Fatal error, SROM halted |
|
|
Read, write, and erase operations may fail if the target block is read or write protected. Block protection levels are set during device programming.
The EraseAll function overwrites data in addition to leaving the entire user Flash in the erase state. The EraseAll function loops through the number of Flash macros in the product, executing the following sequence: erase, bulk program all zeros, erase. After the user space in all Flash macros are erased, a second loop erases and then programs each protection block with zeros.
11.5 SROM Function Descriptions
11.5.1 SWBootReset Function
The SROM function, SWBootReset, is responsible for transi- tioning the device from a reset state to running user code. The SWBootReset function is executed whenever the SROM is entered with an M8C accumulator value of 00h: the SRAM parameter block is not used as an input to the function. This happens, by design, after a hardware reset, because the M8C's accumulator is reset to 00h or when user code executes the SSC instruction with an accumulator value of 00h. The SWBootReset function does not execute when the SSC instruction is executed with a bad key value and a non zero function code. An enCoRe
IILV device executes the HALT instruction if a bad value is given for either KEY1 or KEY2.
The SWBootReset function verifies the integrity of the calibration data by way of a
11.5.2 ReadBlock Function
The ReadBlock function is used to read 64 contiguous bytes from Flash: a block.
The function first checks the protection bits and determines if the desired BLOCKID is readable. If read protection is turned on, the ReadBlock function exits setting the accumulator and KEY2 back to 00h. KEY1 has a value of 01h, indicating a read failure. If read protection is not enabled, the function reads 64 bytes from the Flash using a ROMX instruction and stores the results in SRAM using an MVI instruction. The first of the 64 bytes is stored in SRAM at the address indicated by the value of the POINTER parameter. When the ReadBlock completes successfully the accumulator, KEY1 and KEY2 all have a value of 00h.
Table 11-4. ReadBlock Parameters
Name | Address | Description |
KEY1 | 0,F8h | 3Ah |
|
|
|
KEY2 | 0,F9h | Stack Pointer value, when SSC is |
|
| executed |
BLOCKID | 0,FAh | Flash block number |
|
|
|
POINTER | 0,FBh | First of 64 addresses in SRAM |
|
| where returned data is stored |
Document | Page 16 of 68 |
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