Application Notes
                                 for
                            Mercury 1200
                          (a.k.a. FHR 1200)
                          Intelligent Modem
                                 and
                            NUBYE or IMP

                                 by
                            Roger Warren
                           (San Diego, CA.)

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  NUBYE 
  or IMP.

Hardware Notes

  1)	VERY  IMPORTANT!!  The nomenclature on the case of some of the 
        MERCURY modems 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 yielded 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 IMP.

	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 IMP,  but will  not 
          use  the DTR signal.  In the CLOSED (ANS) position the modem 
          can be used under NUBYE 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!!

IMP installation

        To originate under IMP,  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.

NUBYE installation

	Use under NUBYE is not so straightforward.

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

	USE the following NUBYE EQUATE settings:

	IMODEM	equ	YES	; intelligent modem
	IMAT	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 
        NUBYE  source code.   The combination of EQUATES ANCHOR =  YES 
        and  NODTR = YES causes NUBYE 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!   NUBYE 
        will use the +++ escape sequence. SET SW4 position 2 to OPEN!

Special NOTE:

        Setting  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 NUBYE 
        issues an ascii +++.