6. Configuring the Gateway

If the value of a field from the response of a Modbus slave is different from that configured via AbcConf, the response will be rejected by the gateway. It will then proceed to a re-transmission of the query, provided that at least one re-transmission has been configured for this command (see chapter 6.11.2.2 Configuring the Query, page 72). Of course, this remark does not relate to the data itself, that is to say the Modbus frame fields configured using the “Data location,” “Data length,” and “Byte swap” elements.

Field in the

Size in the

Description

frame

frame

 

Slave Address

1 byte

Identical to that of the query’s “Slave Address” field.

Function

1 byte

Identical to that of the query’s “Function” field.

Register

2 bytes

Identical to that of the query’s “Register” field, since the Modbus response of

 

 

any “Preset Single Register” command is an echo to the corresponding query.

 

 

Here you should also enter the address of the memory object to which the

 

 

command relates.

 

 

E.g.: Enter the value 400, converted to 16#0190 by AbcConf.

Preset Data

2 bytes

Data Location: Address, in the gateway’s input data memory (16#0002 to

 

or more for a

16#00F3), of the item of data received in the “Preset Data” field for the

 

block of data

response’s frame.

 

 

N.B. As far as possible, ensure that the data is located at even addresses in

 

 

order to align the Modbus data (in 16-bit format) on the %IW4.0.x inputs of the

 

 

Profibus-DP coupler.

 

 

E.g.: The value sent back as an echo to the command must be placed in the

 

 

gateway’s input data memory area. We shall use the first two free bytes following

 

 

the input data of the default configuration, i.e. addresses 16#0020-16#0021.

 

 

Data length: Length of the block of input data received in the “Preset Data”

 

 

field of the response frame. It is expressed in number of bytes.

 

 

E.g.: The value of the “Data length” field must be set to 2.

 

 

Byte swap: Identical to that of the query’s “Byte swap” field.

 

 

E.g.: We will also be using the “No swapping” value, for the same reasons as

 

 

with the query.

Checksum

2 bytes

Error check type: Identical to that of the query’s “Error check type” field.

 

 

Error check start byte: Identical to that of the query’s “Error check start bype” field.

 

 

However, these two fields cannot be changed by the user and their values are

 

 

greyed out to reflect this. AbcConf updates the values of these fields

 

 

automatically using those of the query’s “Error check type” and “Error check

 

 

start byte” fields.

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Schneider Electric LUFP7 user manual Start byte fields