Utilities 421
API I/O Access Over TruePort
API I/O Access Over TruePort
You can access IOLAN I/O data through TruePort using the Perle API. The API uses the
command/response format. See the ioapiotp.c sample program, found on the product CD-ROM,
for an example implementation.

API Request Format

All data in the Request must be sent as a single write to the COM port. The API command takes the
following format:

API Response Format

The API command takes the following response format:
Number of Bytes Value
1Function Code (in hexadecimal):
z01—Get read/write boolean register
z03—Get read/write register
z04—Get read only register
z15—Set read/write boolean register (0x0F)
z16—Set read/write register (0x10)
2Starting register number (see A4/T4 Registers , A4D2/A4R2 Registers ,
or D4/D2R2 Registers for this value).
2Number of registers to act on starting from the register defined in byte
2 above.
nData for write. Some values must be read/written as a unit consisting of
2 consecutive registers. If the request is to write, the data to write
follows the number of registers. If accessing registers consisting of 2
bytes or 4 bytes, the data is in big endian (network order) format.
Number of Bytes Value
1Function code of request if no error. Most significant bit will be set if
an error occurred.
1Length of data in response if no error occurred. If an error occurred, the
byte will contain the error code (see the Error Codes table below).
nData response for request (the number of bytes is dependent on the
number and type of registers requested). If the request returns 2 or 4
byte values, it will be in big endian (network order) format. If the
request returns boolean values, the least significant bit (bit 0) represents
the first value requested and bits 1 to 7 represents subsequent boolean
values. If more than 8 boolean registers are requested, they are returned
in successive bytes.