User manual

Chapter 4 Configuration
Page 69 ©February 2009
Supported Modbus Function Codes:
Function Code Meaning
01 Read the state of multiple digital output points
02 Read the state of multiple digital input points
03 Read the value of multiple output registers
04 Read the value of multiple input registers
05 Set a single digital output ON or OFF
06 Set the value of a single output register
07 Read Exception Status - compatibility - returns zero
08
Loopback test - Supported codes
0 return query data
10 clear diagnostic counters
11 bus message count
12 CRC error count
14 slave message count
15 Set multiple digital output points ON or OFF
16 Set multiple output registers
Analog I/O are 16 bit register values. A value of decimal 8192 (hex 2000) represents 0mA. A value
of 49152 (hex C000) represents 20mA. Each 1 mA has a value of 2048 (hex 0800) - a change of
4096 (hex 1000) is equivalent to a change of 2mA. A 4-20mA signal will vary between 16384 (hex
4000) and 49152 (hex C000). A 0-20mA signal will vary between 8192 (hex 2000) and 49152 (hex
C000).
Pulse counts are stored as a 16-bit register. When the register rolls over, from ‘FFFF’ (hex), the
next value will be ‘0001’. The register will only have a value of ‘0000’ when the remote
module starts up, and the previous count is lost. This value will indicate that the counter has
reset.
Modbus Errors
Four Modbus error messages are reported to the Modbus Master. An error response is indicated
by the address of the return message being 128 plus the original slave address.
Supported Exception Codes:
Exceptio
n Code
Name Description
01 Illegal function The module does not support the function code in the query
02 Illegal data address The data address received in the query is outside the
initialized memory area
03 Illegal data value The data in the request is illegal
06 Busy Unable to process message