; Program: T3M-ON1.Z80
; Author:  Joe Wright
; Date:    10 June 1986
;
;	Serial port overlay to TERM III for the Oneac computer.
;	     Z80 DART and 615,385 Hz Baud Rate Generator.
;
MDPORT	EQU	92H		; Z80 sio-0 or dart
M1$DATA	EQU	MDPORT		; Data port
M1$STAT	EQU	MDPORT+1	; Status port
RDA	EQU	1		; Receive data available
TBE	EQU	4		; Transmit buffer empty
DCD	EQU	8		; Data carrier detect
RES	EQU	10H		; Reset external/status
;
; Baud rate table.  Low order byte is baud rate generator divisor,
;  High order byte is the Dart divisor (WR4, 1 stop bit).
;
BD300	EQU	0C400H		; /64, /32
BD1200	EQU	04400H		; /16, /32
BD2400	EQU	08410H		; /32, /8
BD4800	EQU	04410H		; /16, /8
BD9600	EQU	0C420H		; /64, /1
BD19200	EQU	08420H		; /32, /1
BD38400	EQU	04420H		; /16, /1
;
	ORG	600H		; Base address (600h - 6ffh)
;
; Modem Support Package
;
M1$INIT:
	JP	SM1$INIT	; Initialize dart
M1$ISTAT:
	JP	SM1$ISTAT	; Test input status (rda)
M1$OSTAT:
	JP	SM1$OSTAT	; Test output status (tbe)
M1$IN:
	JP	SM1$IN		; Input a byte from the usart
M1$OUT:
	JP	SM1$OUT		; Output a byte to the usart
M1$BREAK:
	JP	SM1$BREAK	; Cause the usart to issue a break
MM1$CST:
	JP	SM1$CST		; Determine carrier status (detect) on usart
M1$SPTAB:
	DB	01111111B	; All rates available
;
;	Modem Routines
;
;  Modem 1 Initialization
;	Function:  To initialize the Modem 1 Port
;	Input Parameters:  A=Speed
;		0=no set
;		1=  300
;		2= 1200
;		3= 2400
;		4= 4800
;		5= 9600
;		6=19200
;		7=38400
;	Output Parameters:  A=Set Speed (same table as above)
;		ZERO FLAG SET
;
SM1$INIT:
	PUSH	HL
	PUSH	DE
	PUSH	BC
	PUSH	AF		; Save all registers
	OR	A
	JR	Z,NO$BAUD	; No speed selected
	CP	8
	JR	NC,NO$BAUD	; Out of range
;
; Set up to determine if desired speed is available
;
	LD	B,A		; Save it a moment
	LD	C,A		; Two copies
	XOR	A		; Clear A
	SCF			; Set carry flag
;
; Shift carry into A (speed) times corresponding to speed table
;
LOOP:	RLA
	DEC	C
	JR	NZ,LOOP		; Shift into position
;
; See if we have a match
;
	LD	HL,M1$SPTAB	; Point to speed table
	AND	(HL)		; Check for corresponding bit
	LD	A,B		; Get speed
	JR	Z,NO$BAUD	; Not available
;
; Speed value in range, set it up
;
	LD	DE,BD300
	DEC	A
	JR	Z,SETBAUD	; Set 300 bps
	LD	DE,BD1200
	DEC	A
	JR	Z,SETBAUD	; Set 1200 bps
	LD	DE,BD2400
	DEC	A
	JR	Z,SETBAUD	; Set 2400 bps
	LD	DE,BD4800
	DEC	A
	JR	Z,SETBAUD	; Set 4800 bps
	LD	DE,BD9600
	DEC	A
	JR	Z,SETBAUD	; Set 9600 bps
	LD	DE,BD19200
	DEC	A
	JR	Z,SETBAUD	; Set 19200 bps
	LD	DE,BD38400
	DEC	A		; Insure A=0, Set 38400 bps
;
; Set up the baud rate requested
;
SETBAUD:
	CALL	SELBNK		; A=0 returns system port data
	AND	0CFH		; Mask rate generator  xx00xxxxB
	OR	E		; Selected rate
	LD	C,A		; Return it in C
	CALL	SELBNK		; A<=>0 sets new rate
	LD	A,4
	OUT	(M1$STAT),A	; Select WR4
	LD	A,D		; Get dart divisor, 1 stop bit
	OUT	(M1$STAT),A
	LD	A,3
	OUT	(M1$STAT),A	; WR3
	LD	A,0C1H		; 8 bits, Rx enable
	OUT	(M1$STAT),A
	LD	A,5
	OUT	(M1$STAT),A	; WR5
	LD	A,0EAH		; DTR, 8 bits, Tx enable, RTS
	OUT	(M1$STAT),A
;
SMINIT$RET:
	POP	AF
ERR$RET:
	POP	BC
	POP	DE
	POP	HL
	OR	A		; Set zero flag
	RET

; Speed value out of range, do nothing, return zero
;
NO$BAUD:
	POP	AF		; Adjust stack
	XOR	A		; A zero
	JR	ERR$RET		; Quit, having failed..
;
; SELBNK  routine in the ON bios gets/sets the baud rate clock
;  This routine also affects the bank port and the terminal speed.
;   Please don't play around with it.
;
SELBNK:
	LD	HL,(1)		; Bios jump table
	LD	L,33H		; Offset to selbnk jump
	JP	(HL)		; Do it, return to caller
;
;  Modem 1 Input Status
;	Function:  To return byte ready (RDA) status
;	Input Parameters:  None
;	Output Parameters:  A=0 if no byte, A=0FFH if byte ready
;
SM1$ISTAT:
	IN	A,(M1$STAT)	; Get status byte
	AND	RDA		; Data available?
	RET	Z		; Zero if no data
	LD	A,0FFH		; Load with ff
	RET
;
;  Modem 1 Output Status
;	Function:  To return buffer empty (TBE) status
;	Input Parameters:  None
;	Output Parameters:  A=0 if buffer full, A=0FFH if buffer empty (TBE)
;
SM1$OSTAT:
	IN	A,(M1$STAT)	; Get status byte
	AND	TBE		; Buffer empty?
	RET	Z		; Zero if not empty
	LD	A,0FFH		; Load with ff
	RET
;
;  Modem 1 Input
;	Function:  To return a byte in the A Reg from Modem 1
;	Input Parameters:  None
;	Output Parameters:  A=byte (MSB NOT cleared)
;
SM1$IN:
	CALL	M1$ISTAT	; Get status
	JP	Z,M1$IN		; Continue until data available
	IN	A,(M1$DATA)	; Get char
	RET
;
;  Modem 1 Output
;	Function:  To output the byte in the A Reg to Modem 1
;	Input Parameters:  A=byte
;	Output Parameters:  None
;
SM1$OUT:
	PUSH	AF		; Save byte
M1OLOOP:
	CALL	M1$OSTAT	; Check output status
	JP	Z,M1OLOOP	; Wait until empty
	POP	AF		; Get byte
	OUT	(M1$DATA),A	; Output it
	RET
;
;  Modem 1 Break
;	Function:  To return the status of the break function for Modem 1
;		and to execute the break if function is available
;	Input Parameters:  A=0 to return status, A=0FFH to break
;	Output Parameters:  A=0 and Zero Flag Set if Break not supported
;
SM1$BREAK:
	XOR	A		; Not implemented
	RET
;
;  Modem 1 Carrier Status Detect
;	Function:  Determine if carrier is present
;	Input Parameters:  None
;	Output Parameters:  A=0 if no carrier, A=0FFH if carrier
;
SM1$CST:
	LD	A,RES		; Reset external/status
	OUT	(M1$STAT),A
	IN	A,(M1$STAT)	; Get new status
	AND	DCD		; Check data carrier
	RET	Z		; No carrier, else..
	OR	0FFH		; Set af
	RET

	DB	'End of Oneac serial port drivers'

	END