Perle Systems Iolan Sds4 Hl Device Server 4030370 User Manual

 293

Modbus I/O Access

If you have a Modbus RTU or Modbus ASCII program, you can access the I/O by connecting to the 
IOLAN over the network.

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. 

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:

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