async-fa.tr3

传真编程的一些文档

	    Page 1			   Document TR30.4.1/89-01001R4
							 January   1989
		      ELECTRONIC INDUSTRIES ASSOCIATION
			 AD HOC SUBCOMMITTEE TR30.4.1

	    Project:  PN-2188, Asynchronous Facsimile DCE Control
		      Standard

	    Source:   Data Race, Inc

	    Subject:  DTE-DCE Interface Description for Facsimile
	    Operations with Minimum DCE Facilities ("Class 1")

	    1.	 Introduction

		 At the September 15, 1988 meeting of the TR30.2.3
	    committee, Les Staples of Data Race was requested to produce
	    a working paper for the "Class 1" DTE-DCE interface for
	    Facsimile Operation embodying the features and facilities
	    agreed upon by the committee.  At the November meeting in
	    Las Vegas, the first draft of that paper was submitted.
	    Many useful suggestions and comments were made at that
	    meeting.  A second draft was presented at the January 1989
	    committee meeting.	The committee has been renamed TR30.4.1.
	    A large number of good suggestions were incorporated,
	    resulting in this, the third draft of that paper.

		 Several changes to the original paper have been made to
	    facilitate a simple 3-wire electrical interface,  to
	    eliminate the need for the DTE to be able to detect and
	    handle the BREAK signal, and to eliminate the requirement
	    for the DTE to be able to force the DCE to Command Mode.

	    The attendees at the January, 1989 meeting were in general
	    agreement on the workability of this paper in this form.
	    The major changes made at the January 1989 meeting were:

		 . requirement for the DCE to support XON/XOFF

		 . removal of NULL padding ability during FAX transmit

		 . add of DCE capability to detect the Final bit in
		   the C-Field of an HDLC frame it is transmitting and
		   to use the Final-bit detection to cause a return to
		   Command Mode.

		 . add of OK response code each time the DCE returns
		   to Command Mode for consistancy.

		 . add of CONNECT response code each time the DCE exits
		   Command Mode while On-Line for consistancy


	    Page 2				    TR30.4.1/89-01001R4

	    2.	 Description of Interface

		 The interface described is an extension of the
	    asynchronous modem control "AT" command set currently under
	    study by the TR30.4 committee and uses the format proposed
	    by the TR30.4 committee.  Every effort has been made to keep
	    this level of interface as simple as possible with minimum
	    requirements for processing placed on the DCE.  The ability
	    to efficiently operate with the current T.4 Recommendation
	    as well as with a future error-protected facsimile
	    transmission protocol, such as that specified in the Revised
	    Recommendation T.4, AP IX-24-E, was also a consideration.

	    An object of this paper is to allow a single port rate
	    setting throughout the facsimile operation.  Port rate
	    setting methodologies are left to PN-2120.

	    Bi-directional flow control is specified in all modes to
	    prevent loss of data.  The DCE must be capable of using in-
	    band (XON-XOFF) and, optionally, electrical lead signaling
	    (RTS-CTS).	Methodologies for specifying to the DCE the flow
	    control method to be used are left to PN-2120.


	    Page 3				    TR30.4.1/89-01001R4

	    2.1  Electrical Interface - Data and Control Signals

		 The described interface assumes a serial asynchronous
	    connection between the DTE and the DCE consisting of, as a
	    minimum, Circuit BA (Transmitted Data), Circuit BB (Received
	    Data), and Circuit AB (Signal Ground).  Circuit CA (Request
	    To Send) may optionally be used by the DTE to flow-control
	    the DCE, and Circuit CB (Clear To Send) may optionally be
	    used by the DCE to flow-control the DTE.  Circuit CD (Data
	    Terminal Ready) may optionally be used by the DTE to control
	    the Off-Hook and Command Mode states of the DCE.  The
	    specific use of these leads are left to PN-2120.

	    2.2  Firmware Interface - Commands and Registers

	    2.2.1     Modulation Control Register

		 The described interface uses a single register to
	    determine the desired modulation type.  This register may be
	    set and examined by the normal ATSr commands.  Register 65
	    has been chosen for this description, but another currently-
	    unused register may be used in its place.  Values in the
	    register select:

		      Value	     Modulation
		       3	V.29 - 7200 BPS
		       4	V.29 - 9600 BPS
		       5	V.27 - 2400 BPS
		       6	V.27 - 4800 BPS
		      10	V.21 -	  300 BPS
		      11	TONE - 2100 Hz (CED)
		      12	TONE - 1100 Hz (CNG - EOM)
		      13	V.33Bis 12000 BPS*
		      14	V.33Bis 14400 BPS*
		      15	V.xx	19200 BPS
		      21   Reserved for DTMF tone detect

	    *These speeds are not required but the values are reserved
	    for future implementations.


	    2.2.2     Dialing and Answering

	    2.2.2.1   Dialing

	    The normal ATD<dial string> is used to dial a facsimile
	    call.  If the DCE is set for CED Tone mode, normal DCE call
	    progress detection and reporting will be used.  When the DCE
	    detects the configured tone, it will send the CONNECT
	    response code to the DTE, followed by the OK response code
	    indicating that the DCE is in Command Mode.


	    Page 4				    TR30.4.1/89-01001R4

	    2.2.2.2   Answering

	    The normal ATA command or Automatic Answering is used to
	    cause the DCE to come off-hook in answer mode.  In facsimile
	    operation, when Register 65 is one of the defined the
	    defined facsimile modes, the CONNECT result code will be
	    immediately sent to the DTE and the DCE will enter Command
	    Mode.  The DTE would normally immediately order the DCE to
	    transmit the 2100 Hz CED tone.

	    2.3.2     Facsimile Transmission and Reception

		 Facsimile transmission and reception is controlled by
	    four commands which are specific to facsimile operation.
	    Since the data set over the interface is asynchronous,
	    containing start and stop bits, it is necessary to set the
	    DTE-DCE interface to a higher data rate than the line
	    modulation rate.  Since the maximum line modulation rate
	    specified in Recommendation T.4 is 9600 BPS, it is
	    convenient to set the DTE-DCE interface rate to 19,200 BPS.
	    The DCE performs buffering and flow-control as described in
	    the remainder of this document.  An object is to allow the
	    entire facsimile operation to be accomplished at a single
	    port rate.	Methodologies for port rate setting are left to
	    PN-2120.


	    Page 5				    TR30.4.1/89-01001R4

	    2.3.2.1 Facsimile Transmit

		 The command AT+FT is used to cause the DCE to transmit
	    using the modulation selected by the content of the
	    Modulation Control Register.  The DCE should be Off-Hook
	    when this command is issued by the DTE.  The DCE will return
	    the CONNECT response code and immediately send the proper
	    training sequence in the selected mode (if any) followed by
	    data.

		 The DCE buffers data in this mode.  The configured
	    flow-control method will be used by the DTE as necessary to
	    pause the DTE.

		 When the DCE's transmit buffer becomes empty, the DCE
	    will stop transmitting, lower transmit carrier, and return
	    to command mode, returning the OK result code.  The DTE may
	    force the DCE to command mode by making Circuit CD (Data
	    Terminal Ready) false, if so configured.  When the DCE
	    returns to command mode, it will lower its transmit carrier.

		 If the mode chosen is TONE, the DCE will immediately
	    begin to send the configured tone when the command is
	    issued.  If the DTE sends any subsequent data to the DCE,
	    DCE will return to command mode.  If the data from the DTE
	    which aborts the receive process is a valid command, the
	    command will be executed correctly.


	    Page 6				    TR30.4.1/89-01001R4


	    2.3.2.2 Facsimile Receive

		 The command AT+FR causes the DCE to enter receive mode.
	    The DCE receives in the modulation mode specified in the