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Accessing I/O Data Via TruePort

286 

IOLAN SDS/SCS/STS/MDC User’s Guide, Version 4.0

There are two groups of commands:

z

Get Commands—Retrieve values of the I/O channel registers

z

Set Commands—Set values on the I/O channel registers. 

All commands need to be written to the COM port as a single write.

I/O Channel registers are all assigned unique addresses, which need to be referenced in all of the 
commands. Please refer to the documentation specific you the applicable mode, for the list and 
addresses of all the registers.

A4

T4

A4D2

A4R2

D4

D2/R2

The following tables show the general structure to be used for Get commands.

Numeric values provided in the API documentation are in Hexadecimal (Hex) format.

1

1

Command Code:

z

0x01 – Get “coils” (Boolean register)

z

0x03 – Get “holding registers” (R/W registers)

z

0x04 – Get “input registers” (R only register)

2-3

2

Starting register number (see 

 

for this value).

4-5

2

Number of registers to read. If this value is greater than 1, the response 
will contain the values of multiple consecutive registers.

1

1

Command that this is a response to. If an error has been detected, the 
command value will have the high bit set (OR with 0x80). For 
example: The command is 0x04, so the command field in the response 
would be 0x84.

2

1

Length of data (in bytes) starting in next byte.

3-n

n

Requested register values.