IAI America REXT - Manual (Page 143)

Part 1 Specification
Chapter 3 Gateway R unit
119
Part 1 Specification
3.9.2 Modbus/RTU Protocol Specification
The RS485 SIO Gateway R unit has an asynchronous serial bus interface conforming to EIA RS485 for interfacing with the
host.
The Modbus protocol is used for communication to receive commands from the host or reference internal information in the
host.
The Modbus protocol is a communication protocol developed by Modicon Inc. (AEG Schneider Automation International
S.A.S.) for PLCs, and its specification is open to the world. For the detailed specifications of this protocol, refer to the
specification document (Modbus Application Protocol Specification V1.1a) published by Modbus-IDA
( http://www.modbus-ida.org/ ), along with this specification.
(1) Basic Specifications
The basic specifications were explained in 3.4.4. Key items are summarized below.
Item Method/condition
Interface Conforming to EIA RS485
Communication method Half-duplex communication
Synchronization method Asynchronous method
Connection pattern 1:1 differential connection
Transmission mode Modbus/RTU
Baud rate (bps)
Selectable from the following by a parameter:
9600, 19200, 38400,
57600, 115200, 230400
Bit length 8 bits
Stop bit 1 bit
Parity None
Caution
In the SIO through mode, 9600 bps and 19200 bps cannot be selected.
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