Filter
Top Products
GFK-0467K Chapter 4 Series 90-30/20/Micro Instructions Set 4-143
4
SVCREQ #6: Change/Read Number of Words to Checksum
Use the SVCREQ function with function number 6 in order to:
• Read the current word count.
• Set a new word count.
Successful execution will occur, unless some number other than 0 or 1 is entered as the requested
operation (see below).
For the Checksum Task functions, the parameter block has a length of 2 words.
To Read the Current Word Count:
Enter SVCREQ function 6 with this parameter block:
0 address
ignored address + 1
After the function executes, the function returns the current checksum in the second word of the
parameter block. No range is specified for the read function; the value returned is the number of
words currently being checksummed.
0 address
current word count address + 1
To Set a New Word Count:
Enter SVCREQ function 6 with this parameter block:
1 address
new word count address + 1
Entering 1 causes the PLC to adjust the number of words to be checksummed to the value given in
the second word of the parameter block. For either the 331 or 311 CPU, the number can be either 0
or 32; in the 211 CPU, the value can be either 0 or 4.
Note
This Service Request is not available on Micro PLCs.