Configuring Serial Ports Using The Commreq Function; Timing; Sending Another Commreq To The Same Port - GE VersaMax PLC User Manual

12.2 Configuring Serial Ports Using the COMMREQ
Function
228 GFK-1503E
For public disclosure
The following tables list the command block values required for setting up a Serial Port
for SNP, RTU, and Serial I/O. All values are in hexadecimal unless otherwise indicated.
The BLKMV commands that are used to create the command block are described in the
example.
It is important to note that 2 parameters have been added to the RTU and Serial IO port
configuration COMMREQ, receive to transmit delay and RTS drop delay. When these
parameters are included in a COMMREQ the data block length must be set to 12H. If a
value of 10H is used, the COMMREQ will still be processed however the receive to
transmit and RTS drop delays would not be recognized. It is also important to note that if
a COMMREQ containing the receive to transmit delay and RTS drop delay is sent to a
CPU that does not support these delay features the CPU will accept and process the
COMMREQ but will ignore the receive to transmit, RTS drop delay, and turnaround
delay (i.e. turn around delay will be ignored only for the RTU and Serial IO protocols in
this case).
Note Either the old form (length 10H) or the new form (length 12H) of the COMMREQ
can be used. Only the new form supports the new parameters.

12.2.1 Timing

If a port configuration COMMREQ is sent to a serial port that currently has an
SNP/SNPX master (for example, the programmer) connected to it, the serial port
configuration specified by the COMMREQ does not take effect until the CPU detects a
loss of the SNP/SNPX master. This occurs the configured T3' time after the master
disconnects. The COMMREQ status word for the port configuration COMMREQ is
updated as soon as the CPU verifies that the specified configuration is valid. That means a
COMMREQ Successful value may be returned by the Port Configuration COMMREQ
before the specified configuration is actually installed.

12.2.2 Sending Another COMMREQ to the Same Port

The application program must wait at least 2 seconds plus the configured T3' time after a
new serial port protocol is installed before sending any COMMREQs specific to that
protocol to the port. This applies to a new protocol installed by Storing a new hardware
configuration or by a port configuration COMMREQ. If the port is configured for Serial
I/O, this waiting period must also follow any Stop to Run mode transition of the CPU.
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