PLX3x Series ♦ Multi-Protocol Gateways
MBS Protocol
User Manual
ProSoft Technology, Inc.
Page 133 of 215
January 25, 2018
Slaves are defined to the system when the gateway loads the
Master Command
List
during start-up and initialization. Each slave defined is set to a state value of
1 in this initial step. If the master port fails to communicate with a slave device
(timeout expired on a command, retries failed), the master sets the state of the
slave to a value of 2 in this status table. This suspends communication with the
slave device for a user-specified
Error Delay Count
.
When the master first suspends polling of a particular slave, it creates an
Error
Delay Counter
for this slave address and set the value in that counter equal to
the
Error Delay Counter
parameter in the configuration file. Then, each time the
gateway scans a command in the list that has the address of a suspended slave,
the gateway decrements the delay counter value. When the value reaches zero,
the gateway sets the slave state to 1. This re-enables polling of the slave.
The first word in the defined register locations contains the status code for slave
node address 1. Each successive word in the list is associated with the next
node in sequence, up to slave node address 247.
7.3.3 MBS Error Codes
These are error codes that are part of the Modbus protocol or are extended
codes unique to this gateway.
Standard Modbus Exception Code Errors
These error codes are generated or returned on both the Controller and slave
ports. These codes are the standard Modbus errors.
Code
Description
1
Illegal Function
2
Illegal Data Address
3
Illegal Data Value
4
Failure in Associated Device
5
Acknowledge
6
Busy, Rejected Message
Gateway Communication Error Codes
These gateway-specific error codes are also returned from the command polling
process and stored in the
Command Error List
memory area.
Code
Description
-1
CTS modem control line not set before transmit
-2
Timeout while transmitting message
-11
Timeout waiting for response after request
253
Incorrect slave address in response
254
Incorrect function code in response
255
Invalid CRC/LRC value in response
