Perle Systems 5500161-40 Format of API Commands, Get Commands, Command Format, Response Format

Accessing I/O Data Via TruePort

Format of API Commands

There are two groups of commands:

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

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

Note: 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.

Model	Go to...
A4	A4/T4 Registers on page 280
T4	A4/T4 Registers on page 280
A4D2	A4D2/A4R2 Registers on page 281
A4R2	A4D2/A4R2 Registers on page 281
D4	D4/D2R2 Registers on page 282
D2/R2	D4/D2R2 Registers on page 282

Get Commands

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

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

Command Format

Byte(s)	# of Bytes	Value
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 A4/T4 Registers on page 280,
		A4D2/A4R2 Registers on page 281, or D4/D2R2 Registers on page 282
		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.

Response Format

Byte(s)	# of Bytes	Value
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.

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