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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
frame
Size in the
frame
Description
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
or more for a
block of data
Data Location: Address, in the gateway’s input data memory (16#0002 to
16#00F3), of the item of data received in the “Preset Data” field for the
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.