ProSoft Technology PTQ-AFC - Manual (Page 176)

Backplane Communication PTQ-AFC ♦ Modicon Quantum Platform
User Manual Liquid and Gas Flow Computer for Hydrocarbon Products
Page 176 of 259 ProSoft Technology, Inc.
June 23, 2011
The Modbus Pass-Thru block received from the module has the following
structure:
Offset Description Type Comments
0 Pass-Thru transaction
present Input
1 Pass-Thru transaction
0-word/1-bit select Input
2 Register Address Input
3 Number of Registers Input
4 to
126 Data. Input When word-swap (Supervisory output word 11) is
applied to a data packet containing an odd number of
words, the last word is swapped with a word of zero.
The Modbus protocol limits the packet to 125 words of
data; the extra word here allows for word-swap to be
applied to a 125-word data packet.
9.1.6 Modbus Master Block
The Modbus master block can be used by the processor to issue a Modbus
master command to a remote Modbus slave device. Configure Port 3 as a
Modbus master device. This block is optional, and must be defined only if the
application intends to use this feature.
The processor must set the following register from the Supervisory Output Block
to 1 in order to issue the Modbus master command to a remote Modbus slave:
Offset Description Type Comments
4 Issue Master Transaction Signal
The Modbus master block configures the Modbus command to be sent to the
remote slave address.
Offset Description Comments
0 Slave Address
1 Direction and register bank
2 Data Item Size and Swap Options
3 Register Address
4 Number of Data Items
5 Error Code
6 to 124
Data