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Sending Commands From a PC Section 5-3
Communications Port Error Flag and Completion Codes CMND(490)
Errors that occur when CMND(490) is used generate a Communications Port
Error Flag and are recorded in a communications port completion code only in
the following cases:
• When a response timeout error has occurred.
• When the number of communications data bytes exceeds the maximum
value for the Unit (i.e., 2,000 bytes for the Ethernet Unit).
• When the actual number of response bytes is greater than the number of
reception bytes that has been set. (The response is not stored in this
case.)
Errors other than these are recorded in the response codes of the responses
stored from the beginning response storage word onwards. Be careful of
these, because there are no Communications Port Error Flags and they are
not recorded in a communications port completion code.
Timing of Communications Flag Changes
• The Communications Port Enabled Flag remains OFF during communica-
tions and turns ON when they are completed (regardless of whether or
not an error occurs).
• The Communications Port Error Flag retains its status until the next trans-
mission or reception.
• The Communications Port Error Flag turns OFF with the execution of the
next communications instruction even if there was an abnormal comple-
tion.
Example
Communications Port Enabled Flag
Communications instruction:
SEND(090), RECV(098), CMND(490)
Communications Port Error Flag
Communications Port Completion Code
Instruction 1
being executed.
Instruction 2
being executed.
Instruction 3
being executed.
0000 (Normal completion)0000 (Normal completion)
(Unit address setting error)
Completion
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