Schneider Electric Modbus Plus Network Bridge Multiplexer none User Manual

Page 45

Configuring the Modbus Models

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Setting the Parameter

You can select `No' or `Yes' for the Modem Booster parameter at any

serial port. The parameter will have the following effect:

If you select `No' for this parameter, incoming commands with function

code 126 or 13 are passed directly to the slave device at the port. If the

command is function code 126, the slave response will be returned to the

originator of the Modbus command after the slave has completed the

requested action, or when it returns an exception response indicating

that it cannot complete the action.

Selecting `Yes' causes the second type of response (function code 13) to

be used. If the command specifies function code 126, the BM85 will

perform a conversion to function code 13 before sending the command to

the slave device. The BM85 will then automatically handle the polling of

the slave device until the command action is completed. It will return

the final response to the originator of the command. The polling process

is handled by the BM85 transparently to the originator.

Modem Booster Example

A P230 programming panel connected to a Modbus Plus networked

controller can access a slave controller that is part of a Modbus network

at a BM85 port. The P230 panel can remotely interrogate, program, and

start the slave controller.

If the Modem Booster parameter is set, the P230 can issue a command

with function code 126. The BM85 converts the function code and sends

the converted command to the slave. The BM85 then handles polling of

the slave, returning a response to the P230 when the slave device's

action is completed.

To the originating device, the response appears as the one from the slave

for function code 126. During this time, however, normal network

transactions can continue between other devices in the user application

and the other slave devices on the BM85 port's Modbus network.

Note:ąFor Modicon 584 Controllers The Modem Booster will not

function with 584 controllers that are in SAFE84 mode. Function code

13 is not recognized by those controllers in that mode. You should

select the Modem Booster `No' option for a BM85 port that will have

584 controllers connected to that port's Modbus network.