Defining The Fax Command Sets; Flow Control; Fax Class 1 At Command Set - ZyXEL Communications COMET 336 User Manual

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TIA PN-2388 Class 2 command set

Defining the Fax Command Sets

The EIA Class 1 and Class 2 fax commands are a set of AT fax commands defined by
EIA/TIA (Telecommunications Industry Association) for controlling fax/modems from a
computer through the serial RS-232 interface. All fax/modems and fax software
supporting this standard will be compatible with each other.
Class 1 commands control how the modem does on-line negotiation while Class 2
commands allow the modem to do many negotiations at once. The Class 1 protocol uses
the modem to transmit fax data only. The complete organizational overhead for this
protocol is handled by the connected computer. The Class 1 command set is also called
the TIA-578 standard.
Several revisions of the class 2 standard exist. Implementations conforming to different
revisions may not work together. A formally approved version is the Class 2.0
command set, also called the TIA-592 standard.

Flow Control

In extended fax AT command mode, the Comet 336 always uses hardware (CTS/RTS)
flow control. The flow control signaling used sending a fax is:
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CTS is used by the Comet 336 to flow control the DTE. When the modem turns
CTS off, the buffer inside the modem is full and cannot accept any more data. The
computer should send data only when CTS is ON.
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RTS is used by the computer to signal the Comet 336 that the fax message is
finished. As soon as RTS off is detected, the modem starts the post message
handshaking to make sure that the remote facsimile has received the fax message
successfully. Then it hangs up the phone and sends a status report to the DTE.
If you want to send a multi-page fax, just add the RTC signal between the fax message of
two pages. The modem detects the RTC signal automatically, handshakes the multi-page
procedure with the remote facsimile and sends the next page message.
The following flow control signaling is used while receiving a fax:
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CTS is not used when receiving fax.
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RTS is used to inform the Comet 336 that the computer cannot accept data at this
moment. The modem will not pass received data to the DTE if RTS is turned off.
When finished receiving the fax message, the Comet 336 will turn off CD then send a
status report result code to the DTE.

FAX Class 1 AT Command Set

Command Options Function & Description Ref.
Fax Operation 43