Technical data

6.28 OB 227: Reading the Checksum of the System Program
Application During cyclic program execution, you can check the contents of the
system program as follows:
•• read the individual memory cells of the system program from
address 0H to address 1DFFFH using OB 226,
•• add all the memory locations using fixed point addition
(operation +F), ignoring overflows,
•• read the checksum using OB 227 and
•• compare the total obtained by the fixed point addition with the
checksum read out by OB 227.
Function The special function organization block OB 227 loads the checksum
of the system program from the memory area of the system into
ACCU 1. The word it reads out corresponds to the total of all memory
cells of the system program from address 0H to address 1DFFFH.
Parameters none
Result - ACCU 1: contains the read out checksum right-justified
(1 word); the remaining contents of ACCU 1
are cleared
- ACCU 2: contains the previous contents of ACCU 1;
the previous contents of ACCU 2 are lost.
Possible errors none
OB 227: Reading the Checksum of the System Program
CPU 928B Programming Guide
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