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Modbus I/O Access

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.
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:
z01 read coils
z03 read multiple holding registers
z04 read input registers
z05 write coil
z06 write single register
z08 diagnostics (echo the request)
z15 force multiple coils
z16 write multiple registers
There are four Modbus data models:
All coil/register values are in decimal.
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.
Network
IOLAN
perle
PC running a
Modbus RTU
or ASCII
Application
UID: 15
I/O Digital
Output
Power