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Modbus I/O Access
278 IOLAN SDS/SCS/STS/MDC User’s Guide, Version 4.0
Modbus TCP Application
If you have a Modbus RTU or Modbus ASCII program, you can access the I/O by connecting to the
IOLAN over the network.
Network
IOLAN
perle
PC running a
Modbus RTU
or ASCII
Application
UID: 15
I/O Digital
Output
Power
Modbus I/O Access
The section defines the function codes and registers you will need to access the I/O through Modbus
TCP, Modbus serial, or Modbus serial/TruePort.
Function Codes
The following function codes are supported by the IOLAN:
z 01 read coils
z 03 read multiple holding registers
z 04 read input registers
z 05 write coil
z 06 write single register
z 08 diagnostics (echo the request)
z 15 force multiple coils
z 16 write multiple registers
There are four Modbus data models:
Discrete Input Not used
Coils Digital Input (DI), Alarm state for DI, Digital Output (DO). All coils
are Boolean values and are 1 byte.
Input Registers (IR) Analog Input (AI), Alarm state for AI. All Input Registers are 2 bytes
long.
Holding Registers Status (R), Control value (R/W or W). Holding Registers with _ENG
registers are 4 bytes long, all other Holding Registers are 2 bytes
long.
All coil/register values are in decimal.