Notes on application MERCURY 1200 (a.k.a. FHR 1200)
                        Intelligent MODEM
                      for IMPxx and BYE5xx


Introduction

  The MERCURY 1200 is a cheapie HAYES clone which is supplied with
  minimal documentation.  The information supplied here is the
  results of some experimentation in the application of the MERCURY,
  and is intended to help those who are trying to use this modem with
  BYE5xx or IMPxx.

Hardware Notes

  1)	VERY IMPORTANT!! The nomenclature on the case of some of the
	MERCURYs is INCORRECT, and NOT ALL are supplied with an errata
	sheet!  From the rear of the device, the connections and switches
	ARE (from left to right): POWER, LINE, PHONE, RS-TTL switch,
	DCE-DTE switch.  The incorrect case markings transpose the RS-TTL
	and DCE-DTE switch!

  2)	SW4- Internal DIP switch:
	Position 2 is called HCD and is documented as follows:
	 In the OFF position (default) Carrier Detect operates independent
	 of the DTR input.  In the ON position Carrier detect is held off
	 until DTR is presented.

	Experimentation has yeilded the following information:
	 With position 2 in the OFF (default) position.  DTR has NO
	 effect on MODEM operation.  The modem escape sequence (if
	 online) followed by the ATH command MUST be used to hang up
	 the phone!
	 With position 2 in the ON position. DTR can be used to hang up
	 the phone and hold off answer.  However, with this setting
         the modem will dial, but will not originate a carrier under IMPxx.

	The author has made the following mod to his modem:
	 SW4 position 2 is left open and a separate switch has been run
	 external to the case and attached in parallel to DIP switch. 
	 I've labelled this ANS/ORIG.  In the OPEN (ORIG) position the
	 modem will ORIGINATE under IMPxx, but will not use the DTR signal.
	 In the CLOSED (ANS) position the modem can be used under BYE5xx
	 using the DTR signal to hang up the phone.

	Of course, you can always leave the case off and change the switch
	 MANUALLY!

	REMEMBER to turn modem power OFF when changing any switch setting!!

IMPxx installation

	To originate under IMPxxx, the switch discussed above should be
	OPEN (in the ORIG mode).  DTR will have no effect on modem operation.
	Under IMP244 , use the NODTR feature to inform IMP.  In previous
	versions, you'll have to code in your own online ESCAPE and
	HANGUP command in the IMP overlay.

BYE5xx installation

	Use under BYE is not so straightforward.

	USE the ANS mode (SW4 position 2 CLOSED) if possible!!!

	USE the following BYE EQUATE settings:

	IMODEM	equ	YES	; intellignet modem
	B5IM	equ	YES	; MODEM uses protocol

	ECHO	equ	NO	; MERCURY does not echo ESC chars,if used
	ANCHOR	equ	YES	; MERCURY ACCEPTS the extended commands,
				; but IGNORES them.  THE ANCHOR subset is
				; sufficient.  ALSO, when answering at
				; 300 BAUD it returns the resutl code at
				; at 300 (as does the ANCHOR)
	HS1200	equ	YES	;
	NODTR	equ	NO	; use the DTR line to hang up
	NOATA	equ	NO	; MERCURY USES ATA
	SHORTB	equ	xx	; doesn't matter, use NO.

NOTE:	If you MUST use NODTR equ YES then you'll have to edit the BYE
	source code.  The combination of EQUATES ANCHOR = YES and NODTR = YES
	causes BYE to initialize the modem with an escape character of 128d
	(80h).  While the MERCURY ACCEPTS the setting, sending three bytes
	of 80h (preceeded and followed by a 1 second pause) does not
	cause an online escape.  Change the code to eliminate the S2=128
	initialization command!  BYE will use the +++ escape sequence.
	SET SW4 position 2 to OPEN!

A Special NOTE to Wayne Masters:
	The difficulty mentioned in the above paragraph needs your
	attention, as the settings ANCHOR=YES and NODTR=YES will currently
	cause a combination where the modem (not just the MERCURY) is
	programmed as having the escape character as 80h, while BYE issues
	an ascii +++.

That's all.

Roger Warren, San Diego, CA.
NOV, '85