NAiS FP Series, User Manual

Page: 152 / 326

FP
Σ
8.1 Computer Link
8 - 7
4
Check code
This is the BCC (block check code) used to detect errors using horizontal parity. The BCC
starts from the start code and checks each character in sequence, using the exclusive OR
operation, and replaces the final result with character text.
5
End code (Terminator)
There is always a “
C
R
” (ASCII code: H0D) at the end of the message.
Notes
Precautions when reading data
If no response is returned, the command may not have arrived
at the PLC, or the PLC may not be functioning. Check to make
sure all of the communication specifications, such as the
communication speed, data length, and parity, match between
the computer and the PLC.
If the received response contains a “!” instead of a “$”, the
command was not processed successfully. The response will
contain a communication error code, so confirm the content of
the error.
The unit number and command name will be the same for a
command and its corresponding response, as shown in the
figure below. This makes the correspondence between the
command and the response clear.
Command %
0 1 # R C
C
R
Same Same
Response
% 0 1 $ R C
C
R
Figure 146: FP
Σ
Command & response message (note)