; TRS-80 Model 4p internal modem overlay for MEX: revision 1.4
; Originally written: 04/16/84 by Ronald G. Fowler (V1.0)
;
; 11/22/85: Changed all portions of this code that are strictly for the
;           smartmodem so that this overlay will work with the TRS-80
;           Model 4p internal modem. (Bob Kitchen)
;
; The following notes are provided as information about the modification
; history of this overlay:
;
; 07/16/84: Added equate NUMRES to enable/disable numeric result code 
;	    interpretation.  Under TurboDos, the first digit of the 
;	    phone number was being interpreted as a result code as it 
;	    was echoed by the Anchor modem as it dialed.  Set NUMRES false
;	    to disable numeric results. (Bob Puckett)
;
; 06/06/84: Fixed problem for Anchor users, where, when the modem returned
;	    "DIAL TONE", the "N" in "TONE" was being regarded as a NO-CONNECT
;	    code.  Now we flush the entire result line before reading another.
;	    Also added code for numeric version of "CONNECT 1200".  --RGF
;
; Small bug repaired: (V1.1) 05/14/84 (Steve Grandi): Smartmodem was not being 
;	flushed after a dial string so that last digit of the phone number 
;	was being interpreted as a numeric result code causing the program, 
;	for certain numbers, to give up even as the modem merrily dialed away.
;
; This module adapts MEX for the TRS-80 Model 4p internal modem.  The main
; function is to provide dialing capability; the disconnect vector is
; ancillary.  You may use this module as a model to develop dialing routines
; for other Radio Shack modems.  The only pertinent entry point is the DIAL
; routine; you'll find entry specs for that below.
;
; This overlay will work with any modem overlay that terminates prior to 0B00H
;
FALSE	EQU	0
TRUE	EQU	NOT FALSE
;
; SYSTEM CONSTANTS
;
TPULSE	EQU	0105H		;TONE/PULSE FLAG IN MODEM OVERLAY
DIALV	EQU	0162H		;LOCATION OF DIAL VECTOR IN OVERLAY
DIALOC	EQU	0B00H		;DIALING CODE GOES HERE
MEX	EQU	0D00H		;"CALL MEX"
;
; FOLLOWING ARE FUNCTION CODES FOR THE MEX SERVICE CALL PROCESSOR
;
INMDM	EQU	255		;RETURN CHAR FROM MDM IN A, CY=NO CHR IN 100MS
TIMER	EQU	254
TMDINP	EQU	253		;B=# SECS TO WAIT FOR CHAR, CY=NO CHAR
CHEKCC	EQU	252		;CHECK FOR ^C FROM KBD, Z=PRESENT
SNDRDY	EQU	251		;TEST FOR MODEM-SEND READY
RCVRDY	EQU	250		;TEST FOR MODEM-RECEIVE READY
SNDCHR	EQU	249		;SEND A CHARACTER TO THE MODEM (AFTER SNDRDY)
RCVCHR	EQU	248		;RECV A CHAR FROM MODEM (AFTER RCVRDY)
;
CR	EQU	13
LF	EQU	10
;
	ORG	DIALV		;OVERLAY THE DIALING VECTOR
	JMP	DIAL
;
; This is the DIAL routine called by MEX to dial a digit. The digit
; to be dialed is passed in the A register.  Note that two special
; codes must be intercepted as non-digits: 254 (start dial sequence)
; and 255 (end-dial sequence).  Mex will always call DIAL with 254
; in the accumulator prior to dialing a number.  Mex will also call
; dial with 255 in A as an indication that dialing is complete. Thus,
; the overlay may use these values to "block" the number, holding it
; in a buffer until it is completely assembled (in fact, that's the
; scheme employed here for the Smartmodem).
;
; After the 254-start-dial sequence, MEX will call the overlay with
; digits, one-at-a-time.  MEX will make no assumptions about the dig-
; its, and will send each to the DIAL routine un-inspected (some modems,
; like the Smartmodem, allow special non-numeric characters in the
; phone number, and MEX may make no assumptions about these).
;
; After receiving the end-dial sequence (255) the overlay must take
; whatever end-of-dial actions are necessary *including* waiting for
; carrier at the distant end.  The overlay should monitor the keyboard
; during this wait (using the MEX keystat service call), and return
; an exit code to MEX in the A register, as follows:
;
;	0 - Carrier detected, connection established
;	1 - Far end busy (only for modems that can detect this condition)
;	2 - No answer (or timed out waiting for modem response)
;	3 - Keyboard abort (^C only: all others should be ignored)
;	4 - Error reported by modem
;
; <No other codes should be returned after an end-dial sequence>
;
; The overlay should not loop forever in the carrier-wait routine, but
; instead use either the overlay timer vector, or the INMDMV (timed 100
; ms character wait) service call routine.
;
; The DIAL routine is free to use any of the registers, but must return
; the above code after an end-dial sequence
;
	ORG	DIALOC
;
DIAL:	LHLD	DIALPT		;FETCH POINTER
	CPI	254		;START DIAL?
	JZ	STDIAL		;JUMP IF SO
	CPI	255		;END DIAL?
	JZ	ENDIAL		;JUMP IF SO
;
; Not start or end sequence, must be a digit to be sent to the modem
;
	MOV	M,A		;PUT CHAR IN BUFFER
	INX	H		;ADVANCE POINTER
	SHLD	DIALPT		;STUFF PNTR
	RET			;ALL DONE
;
; Here on a start-dial sequence
;
STDIAL:	LXI	H,DIALBF	;SET UP BUFFER POINTER
	SHLD	DIALPT
	RET
;
; Here on an end-dial sequence
;
ENDIAL:	MVI	M,'X'		;4P MODEM START DIAL CHARACTER
	INX	H
	MVI	M,CR		;STUFF END-OF-LINE INTO BUFFER
	INX	H		;FOLLOWED BY TERMINATOR
	MVI	M,0
	LXI	H,SMDIAL	;POINT TO DIALING STRING
	CALL	SMSEND		;SEND IT
WAITSM:	MVI	C,INMDM
	CALL	MEX		;CATCH ANY OUTPUT FROM THE MODEM
	JNC	WAITSM		;LOOP UNTIL NO MORE CHARACTERS
;
; THE FOLLOWING LOOP WAITS FOR A RESULT FROM THE MODEM (UP TO
; 30 SECONDS: YOU MAY CHANGE THIS VALUE IN THE FOLLOWING LINE).
;
RESULT:	MVI	C,30		;<<== MAXIMUM TIME TO WAIT FOR RESULT
SMWLP:	PUSH	B
	MVI	B,1		;CHECK FOR A CHAR, UP TO 1 SEC WAIT
	MVI	C,TMDINP	;DO TIMED INPUT
	CALL	MEX
	POP	B
	JNC	SMTEST		;JUMP IF MODEM HAD A CHAR
	PUSH	B		;NO, TEST FOR CONTROL-C FROM CONSOLE
	MVI	C,CHEKCC
	CALL	MEX
	POP	B
	JNZ	SMNEXT		;IF NOT, JUMP
	MVI	B,CR		;YES, SHUT DOWN THE MODEM
	MVI	C,SNDCHR
	CALL	MEX
	MVI	A,3		;RETURN ABORT CODE
	RET
SMNEXT:	DCR	C		;NO
	JNZ	SMWLP		;CONTINUE
;
; ONE HALF MINUTE WITH NO MODEM RESPONSE (OR NO CONNECTION)
;
SMTIMO:	MVI	A,2		;RETURN TIMEOUT CODE
	RET
;
; MODEM GAVE US A RESULT, CHECK IT
;
SMTEST:	ANI	7FH		;IGNORE ANY PARITY
	CALL	SMANAL		;TEST THE RESULT
	MOV	A,B		;A=RESULT (CY SIGNIFICANT HERE TOO)
	PUSH	PSW		;SAVE IT
SMTLP:	MVI	C,INMDM		;FLUSH ANY REMAINING COMMAND LINE
	CALL	MEX
	JC	SMCHEK		;JUMP IF NO INPUT
	CPI	LF		;GOT SOME ... WAITING FOR EOL
	JNZ	SMTLP		;EAT ANY IN-BETWEEN
SMCHEK:	POP	PSW		;A HAS MEX RETURN-CODE, CY=1 IF UNKNOWN
	JC	RESULT		;IF RESULT UNKNOWN, IGNORE IT
	RET
;
SMANAL:	MVI	B,0		;PREP CONNECT CODE
	CPI	0AH		;4P MODEM CONNECT CODE
	RZ
	INR	B		;PREP NO CONNECT CODE
	CPI	15H		;4P MODEM NO CONNECT CODE
	RZ
	STC			;UNKNOWN...
	RET
;
; 4P MODEM UTILITY ROUTINE: SEND STRING TO MODEM
;
SMSEND:	MVI	C,SNDRDY	;WAIT FOR MODEM READY
	CALL	MEX
	JNZ	SMSEND
	MOV	A,M		;FETCH NEXT CHARACTER
	INX	H
	ORA	A		;END?
	RZ			;DONE IF SO
	MOV	B,A		;NO, POSITION FOR SENDING
	MVI	C,SNDCHR	;NOPE, SEND THE CHARACTER
	CALL	MEX
	JMP	SMSEND
;
; DATA AREA
;
SMDIAL:	DB	'*C*MG@',125,'DT'
DIALBF:	DS	52		;2* 24 CHAR MAX, + CR + NULL + SLOP
DIALPT:	DS	2		;DIAL POSITION POINTER
;
	END
DIAL:	DB	'*C*MG@',125,'DT'
DIALBF:	DS	52		;2* 24 CHAR MAX, + CR + NULL