Additions to User Manual
The following will be added to the
IC69* PLC Serial Communications User’s Manual
at its next revision
Disable Break-Free SNP Slave Operation COMMREQ: 7004
Available Modes: Slave
Local command. This command disables the break-free SNP feature in IC693 CPU firmware version
8.20 and later versions. Break-free SNP simplifies MODEM communication with IC693 PLCs by
eliminating the requirement for a serial break at the start of each SNP and SNP-X session.
Break-free SNP on built-in slave ports in PLC CPUs uses a small fraction of the CPU processing
bandwidth. For most applications the impact on CPU performance is negligible. However, applications
that use multi-drop SNP or SNP-X communication can incur noticeable increases in PLC sweep times
because all slave units must examine every received message.
This command disables break-free operation and eliminates its impact on PLC sweep time. Break-free
operation remains disabled until the next time the PLC is powered on or command 7005 is executed. If a
communication session is in progress when the command is executed, communication will continue, but
detection of no-break Attach/X-Attach messages will stop immediately.
The COMMREQ that sends this command may be executed on the first PLC sweep.
If the COMM_REQ status word location specified in words 3 and 4 of the command block is not a valid
%R, %AI or %AQ reference, power flow into the COMM_REQ function block will cause power flow to its
fault (FT) output. Otherwise, the value one (1) is written to the status word when the command succeeds.
When unsuccessful, one of these values is returned:
010Ch WAIT-mode COMREQ is not permitted; must use NOWAIT.
020Ch Command not supported; the port is either not configured as an SNP
slave or does not support break-free operation.
Sending this command when break-free SNP is alr
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