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4-162 Series 90-30/20/Micro Programmable Controllers Reference Manual – September 1998 GFK-0467K
4
SVCREQ #23: Read Master Checksum
Use SVCREQ function #23 to read the master checksums for the user program and the
configuration. The SVCREQ output is always set to ON if the function is enabled, and the output
block of information (see below) starts at the address given in parameter 3 (PARM) of the
SVCREQ function.
When a RUN MODE STORE is active, the program checksums may not be valid until the store is
complete. Therefore, two flags are provided at the beginning of the output parameter block to
indicate when the program and configuration checksums are valid.
For this function, the output parameter block has a length of 12 words with this format:
Master Program Checksum Valid (0 = not valid, 1 = valid) address
Master Configuration Checksum Valid (0 = not valid, 1 = valid) address + 1
Number of Program Blocks (including _MAIN) address + 2
Size of User Program in Bytes (DWORD data type) address + 3
Program Additive Checksum address + 5
Program CRC Checksum (DWORD data type) address + 6
Size of Configuration Data in Bytes address + 8
Configuration Additive Checksum address + 9
Configuration CRC Checksum (DWORD data type) address + 10
Example:
In the following example, when input %I0251 is ON, the master checksum information is placed
into the parameter block, and the output coil (%Q0001) is turned on. The parameter block is
located at %R0050.
| _____
|%I0251 | | %Q0001
|——| |———| SVC_|——————————————————————————————————————————————————————————( )—
| | |
| | REQ |
| | |
| CONST —|FNC |
| +0023 | |
| | |
|%R0050 —|PARM |
| |_____|
|