User`s manual

Western Reserve Controls 1782-JDM User’s Manual
PUB 24.0
7
Each time a new message is received at the JDM from the Modbus network, it will increment the
counter.
7. The second byte of the record will be a status byte. This is a combination of the status of the received
Modbus message and the JDM’s error detection system.
A typical response is as follows:
•
Record count or sequence number (1 byte)
•
Status / error data (1 byte)
•
Device’s Modbus address (1 byte)
•
Modbus command number (1 byte)
•
Modbus error/status value (1 byte)
•
Starting Modbus register address (2 bytes)
•
Number of data bytes (1 byte)
•
Input data (2 bytes per datum value)
•
1
st
Register data (2 byes)
•
2
nd
Register data (2 byes)
•
3
rd
Register data (2 byes)
2.5 How to Write Modbus Device Output Data
1. Configure the port to send output data by setting the size of the poll output buffer at the Master to
reflect the number of ASCII output bytes that will be sent to the ASCII.
2. Perform a poll function to the ASCII. ASCII data will be sent to the ASCII. The first byte of the field
must be a “record number”, which the host application must increment each time a new record is to
sent from the ASCII to the Modbus device. The bytes following this will be the ASCII data being sent to
the ASCII device.
The data sent to the JDM will
typically
contain the following info:
•
Record sequence number (1 byte)
•
Device’s Modbus address (1 byte)
•
Modbus command number (1 byte)
•
Beginning Register number (2 byes)
•
Number of registers (2 bytes)
•
Output data (2 bytes per datum value)