Perle Systems STS User Manual
Accessing I/O Data Via TruePort
276
IOLAN SDS/SCS/STS User’s Guide, Version 3.6
Format of API Commands
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.
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.
commands. Please refer to the documentation specific you the applicable mode, for the list and
addresses of all the registers.
Get Commands
The following tables show the general structure to be used for Get commands.
Command Format
Response Format
Note:
All commands need to be written to the COM port as a single write.
Model
Go to...
A4
T4
A4D2
A4R2
D4
D2/R2
Note:
Numeric values provided in the API documentation are in Hexadecimal (Hex) 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
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.
will contain the values of multiple consecutive registers.
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.
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.