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CY7C63310, CY7C638xx
Document 38-08035 Rev. *K Page 15 of 83
Two important variables that are used for all functions are KEY1
and KEY2. These variables are used to help discriminate
between valid SSCs and inadvertent SSCs. KEY1 must always
have a value of 3Ah, while KEY2 must have the same value as
the stack pointer when the SROM function begins execution.
This would be 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
9.4.1 Return Codes
The SROM also features Return Codes and Lockouts.
Return codes aid in the determination of 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.
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 all the user space in all the Flash macros are erased, a
second loop erases and then programs each protection block
with zeros.
9.5 SROM Function Descriptions
9.5.1 SWBootReset Function
The SROM function, SWBootReset, is the function that is
responsible for transitioning 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 the user
code executes the SSC instruction with an accumulator value of
00h. The SWBootReset function is not executed when the SSC
instruction is executed with a bad key value and a non-zero
function code. An enCoRe II 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 16-bit checksum, before releasing the M8C to
run user code.
9.5.2 ReadBlock Function
The ReadBlock function is used to read 64 contiguous bytes
from Flash: a block.
This function first checks the protection bits and determines if the
desired BLOCKID is readable. If the 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 the
SRAM using an MVI instruction. The first of the 64 bytes are
stored in the 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 9-2. 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
Table 9-3. 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.
Table 9-4. 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 must be stored.
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