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Appendix N
Hayes Modem AT Command Protocol
The Hayes Modem AT Command Protocol is used to make various settings or control remotely a Hayes modem
connected to the Serial Communications Board via RS-232C cable.
Protocol Configuration
The configuration of the Hayes Modem AT Command Protocol is shown below.
Sequence Communications Function
Ladder interface
No. sequence name
Send word
allocation
Receive word
allocation
550 Initialize modem
(general-purpose)
Initializes the modem connected to the
Serial Communications Board. The
initialization command is set in the words
specified for the second operand of
PMCR.
Yes No
560
570
580
Initialize modem
(specialized)
Initializes certain OMRON Modems. No No
561
571
581
Dial Dials from the modem connected to the
Serial Communications Board. AT
commands and telephone numbers are set
set in the words specified for the second
operand of PMCR. This sequence can be
used only for certain OMRON modems.
Yes No
552 Password After the line is connected, the password
sent from the other exchange is verified to
confirm that the line is connected to the
desired exchange. The normal value of a
password is set in the words specified for
the second operand of PMCR.
Yes No
553 Data send/receive
(general purpose
sequence)
Sends arbitrary data to the exchange
which the line is connected. Send data is
set in the words specified for the second
operand of PMCR. Receive data is stored
in the words specified for the third operand
of PMCR.
Yes Yes
554 Escape Shifts the modem to escape mode (the
condition in which command input is
available during data communications).
The escape code is fixed to “+++”
No No
555 Hang up After shifting to escape mode, the line is
disconnected.
No No
562
572
582
Initialize and dial
Executes continuously from initialization to
dialling operations for certain OMRON
Modems.
Yes* No
590 Escape to hang up Executes continuously from shifting to the
escape mode to hanging up.
No No
Note 1. Ladder Interface Settings
YES: User settings are required for the 2nd and 3rd operands of PMCR.
NO: Send word allocation: Set a dummy word address for the 3rd operand (D).
Receive word allocation: Set the constant 0000 for the 2rd operand (S).
2. For details about dialling, refer to sequences 561, 571 and 581.