User Manual
Chapter 11
GFK-1503F
Jan 2020
The Service Request Function
183
11.7
Change/Read Number of Words to Checksum
Use SVCREQ 6 to read or change the number of words in the program to be checksummed.
The function is successful unless some number other than 0 or 1 is entered as the requested
operation.
11.7.1
Parameter Block Formats for SVCREQ 6
The parameter block has a length of 2 words.
To read the word count, the first word of the parameter block must contain a zero:
Figure 182
The function returns the current word count in the second word of the parameter block.
Figure 183
To change the word count, the first word of the parameter block must contain a one:
Figure 184
The PLC will change the number of words to be checksummed to the new value.
Example of SVCREQ 6
In the example, when enabling contact FST_SCN is set, the parameter blocks for the
checksum function are built. Later in the program, if input %I0137 turns on, the SVCREQ
reads the number of words being checksummed. The parameter block for the Read function
is located at %R0150-151. The ADD function adds 32 to the current word count in %R0151
and places the result in %R0153. The parameter block for the Change function is located at
%R00152-153. The second SVCREQ then changes to the new word count specified in
%R0153.
