PLX3x Series ♦ Multi-Protocol Gateways MBS Protocol
User Manual
ProSoft Technology, Inc. Page 129 of 215
January 25, 2018
Slave Port: General Port State and ComState Status
Note: There are two additional port status parameters that are not available from the General
Modbus Error and Status Data area. The status values, Port State and Port ComState (circled in
red in the graphic below), can be found only in the PCB diagnostic menus under Comm Status for
a port.
These status values are state registers. They are used as "scratchpad" areas by
the gateway firmware to keep track of the current logical state of activities on a
slave port. These state registers are constantly changing as the gateway
progresses through the various stages needed to process communication on the
serial ports. This processing happens faster than can be followed, unless a port
error causes the value to remain constant for some noticeable length of time.
The diagnostic screen display a snapshot of the data; that is, the current values
at the time they are displayed, but the module does not update the data. They
are not live-data screens. Therefore, to see a change in State or ComState, you
must repeatedly update the screen by pressing the appropriate menu key to have
the screen refreshed. Depending on the refresh timing you may or may not see a
change in the displayed values every time you call for an update.
The State register may display any of the following values:
Preparing port, Flushing all buffers, Scan for RTS-Off, or Waiting for port
enable signal
Waiting for receipt of data
Receiving a message from the Master
Building a slave response message
Modbus master is fetching next command
Sending slave response to the Master
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