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GFK-0467K Chapter 4 Series 90-30/20/Micro Instructions Set 4-119
4
• In a particular program, there can only be one Sequential Event Recorder function block that
can be associated with each command and data block.
• If the user selects an input module to be scanned the PLC will NOT verify the module is a
DISCRETE INPUT MODULE, or that any Channel Descriptions associated with the module
have valid lengths and offsets based upon the module size. The user is responsible for
correctly setting up the sampling of an Input Module.
• If an input module is selected to be scanned, it is only scanned once per function block
execution. Multiple channel descriptions can target the input module, but the scanning is still
only performed once per function block execution.
• If the user requires x channels where x is not equal to 8, 16, 24, but is less than 32 they must
select a number of channels which is greater than x and a multiple of 8 and then fill in a null
channel description for the remaining unused channels. A null channel description has a
segment selector of 0xFFh, a length parameter which must equal the number of unused
channels, and a 0 offset.
• The SER can be used in a periodic subroutine, however caution should be used when doing so.
Depending on the mix of the samples being collected, the SER could take more than 1msec to
execute and therefore it would not be practical to use it inside of a 1msec periodic subroutine.
It will function exactly as any other function block does in the periodic subroutine, it is
evaluated and executed according to the Boolean input logic.