TITLE	'Bit Banger for CompuPro DISK1'
;	Bit Banger for CompuPro DISK1.


;	7 Data bits, no parity
;	For 2 MHz 8085, use 300 Baud.
;	For 5 MHz,	use 600 Baud.
	space	4,10
;	Normal bit timings.
;				___ TICK ___
;	Baud	uSec/bit	2MHz	5MHz
;	4800	208		<<<	25
;	2400	416		18	46
;	1200	833		38	92
;	600	1667		75	216
;	300	3333		102	>>>
;	110	can't		>>>	>>>
;
;	Restriction on higher rates is due to the fact
;	that we can only adjust speed by integral TICK
;	counts: Unless number > 100, cannot tune in closer
;	than one percent.
 
 
 
 
;	Timing for the Bit Banger is via programmed delays,
;	so be very careful if changes are contemplated.
;	Baud =	Bit per second of serial data.
;	Cycle =	Machine cycle (clock period, T-State).
;	Tick =	1/n of a bit time (PERIOD of sample).
;
;	1200 baud	= 833 uSec/bit
;	* 2 MHz		= 1667 cycles/bit
;	/ 16 sample rate= 104  cycles/Tic

yBANG:	EQU	SER	;Serial bit latch port


	DS	1	;Banger Threshold (= 0.5 * TICK)
TICK:	DS	1	;Banger sample period
SAMP:	DB	-1	;dummy pre-store
	DS	10	;buckets for Space counts
	DB	-1
	space	4,10
;	CONSOLE STATUS
;	BitBanger has no status available, so always
;		replies NO.  This means that Ctrl-S will
;		not work when using the BitBanger.
;	Exit	A= FFh	means character available.
KONST:
	XOR	AX,AX	;A=0, clear Carry
	RET
	space	4,10
;	Output 1 Character.
;	Entry	CL= Character to output.
;		Line assumed marking.
;	Exit	Line marking, but stop time not elapsed.
;	Transmission format:
;		Data bits inverted;
;		Start(0), D0, D1, ..., D6, Stop(1), Leaves marking
;	Note: Cannot destroy DX or BX.
;	Uses	AF, CX.
KONOUT:
	proc
	PUSH	BX
	PUSH	DX
	MOV	AL,CL
	AND	AL,# 7Fh	;use Bit7 as Start bit (0)
	XOR	AL,# 0FFh	;invert data
	RCL	AL	;adjust
	MOV	CL,AL
	LD	CH,# 7+1+1	;7 bit data, 1 Start, 1 fudge

;	Write 8 bits.
:N:
	LD	AL,TICK	;(7	7
	MOV	DL,AL	;(2)
;r	STO	DH,[bx]	;(7	7
;r	LD	DH,# 0	;(7	7
	MOV	AL,CL	;(2)
	RCR	AL	;(2)
	MOV	CL,AL	;(2)
	DEC	CH	;(2)
	JZ	:6	;if enuf bits read
	INC	BX	;(5	6

;	Begin output loop for this bit.
:M:
	OUTB	yBANG	;(10)
	AND	AL,# 80h	;(4)
	RCL	AL	;(2)
	RCR	AL	;(2)
	MOV	DH,AL	;(2)
	DEC	DL	;(2)	4)
	JNZ	:M	;(7)		;if not yet one bit time
	JMP	:N


:6:
	LD	CH,# 2	;2 Stop bits
:62:
	LD	AL,TICK
	MOV	DL,AL
	INC	DL
:65:
	LD	AL,# 0	;Stop bit= Mark= 1
	OUTB	yBANG	;(10)
	AND	AL,# 80h	;(4)
	RCL	AL	;(2)
	RCR	AL	;(2)
	MOV	DH,AL	;(2)
	DEC	DL	;(2)	4)
	JNZ	:65	;(7)
	DEC	CH
	JNZ	:62	;if more stoppers
	POP	DX
	POP	BX
	RET
	space	4,10
;	Bit Banger Input.
;
;	Exit	A= Character read.
;			Bit7 clear.
;	Uses	AF, CX, DX, BX.

;	Timing for	8086	8088
KONIN:
	if	@ldr <> 4
	proc
	LD	BX,# SAMP
	LD	CH,# 9+1

;	Wait for Start bit.
:L0:
	INB	yBANG
	RCL	AL	;(2)
	JNC	:L0	;if line still Marking

;	Now take 7 uniform samples.
;	The number of peeks in each determines the sample width.
:N:
	LD	AL,TICK	;(13	13
	MOV	DL,AL	;(2)
	STO	DH,[bx]	;(7	7
	LD	DH,# 0	;(7	7
	DEC	CH	;(2)
	JZ	:6	;(10)	if enuf bits read
	INC	BX	;(5	6

;	Begin sampling loop for this bit.
:M:
	INB	yBANG	;(10)
	AND	AL,# 80h	;(4)
	RCL	AL	;(2)
	ADD	AL,DH	;(2)
	MOV	DH,AL	;(2)
	DEC	DL	;(2)	4)
	JNZ	:M	;(7)
	JMP	:N	;(7)


;	Reduce sample counts to data bits.
;	Note that due to DISK1 inversion,
;	0  Space =	Count[i]  >  Threshold
;	1  Mark  =	Count[i]  <  Threshold
;	Actually, all counts "near" mid-range are probably
;	errors.
:6:
	LD	BX,# SAMP+8	;-> Data bit 6
	LD	AL,TICK-1
	MOV	DH,AL	;C= Threshold for Mark versus Space
	LD	CX,# rev 7
:64:
	MOV	AL,CL
	RCL	AL	;(2)
	MOV	CL,AL
	LD	AL,[bx]
	CMP	AL,DH
	JNC	:66	;if large count
	INC	CL	;set bit for Mark
:66:
	DEC	BX
	DEC	CH
	JNZ	:64	;if more bits to reduce
	MOV	AL,CL
	endif
	RET
	space	4,10
;	Determine speed of terminal.
;	User must input a 'U'
;	Relies on being able to measure the width of the
;	Start bit.  Therefore, needs an odd-numbered Ascii
;	to be input.
;	Consecutive samples look like this:
;		...11111111111110000..001xxxxxxx...
;		Mark		Space	Mark
;		...Idle		Start	Data0	(ignore...)
BAUD:	proc
	LD	BX,# SAMP
	LD	CH,#3
	LD	DX,#1

;	Wait for Start bit.
:L0:
	INB	yBANG
	RCL	AL	;(2)
	JNC	:L0	;if line still Marking

;	Now measure width of next several pulses.
;	The number of peeks in each determines the sample width.
:N:
	MOV	CL,DL	;(2)
	LD	AL,TICK	;(13	13
	STO	DH,[bx]	;(7	7
	LD	DH,#0	;(7	7
	DEC	CH	;(2)
	JZ	:6	;(10)	if enuf bits read
	INC	BX	;(5	6


;	Begin sampling loop for this bit.
:M:
	INC	DH	;(2)
	INB	yBANG	;(10)
	AND	AL,# 80h	;(4)
	RCL	AL	;(2)
	CMP	AL,CL	;(2)
	MOV	DL,AL	;(2)
	JZ	:M	;(7)
	JMP	:N	;(7)


;	Reduce sample counts to data bits.
:6:
	LD	AL,SAMP+1
	STO	AL,TICK	;set nominal bit width
	CLC
	ROR	AL	;width / 2 = threshold
	STO	AL,TICK-1
	RET



;	Endx	GBcbiot3.asm