autobaud.asm

8051 UART autoset Baudrate

;
;****************************************************************************
;
;  Purpose:
;	Automatically Detect The Baud Rate On The Serial Port
;
;  Date:
;	02/03/95
;
;  Author:
;	John C. Wren
;
;  Modications:
;	02/04/97 - Added Description Fields For Archive
;
;  Processor:
;	Generic 8031, Running At 11.0592MHz
;
;  Assembler:
;	Avocet AVA51
;
;  Dependencies:
;	None
;
;  Files:
;	None
;
;  Philosophic:
;	These Routines Make The Assumption That The Entire CPU Can Be
;	Dedicated To Determing The Baud Rate Of The Serial Port.  This
;	Could Be Better Implemented By Tying The Serial Port RX Pin To 
;	-INT0 Or -INT1.  This Would Allow An Interrupt To Be Generated
;	On The Edge Of The Start Bit, Rather Than The Autobauder Camping
;	Out On The Port Pin, Waiting For The Change.
;
;	This Routine Came From A FORTH Interpeter I Wrote.  Since The System
;	Didn't Have To Do Anything While Waiting For The Serial Port To
;	Autobaud, It Was OK To Camp Out On The Serial Port Pin.  This Is
;	Not Very Elegant.
;
;****************************************************************************
;
;  Includes
;
		seg	code
;
;****************************************************************************
;
;  Publics
;
		public	AUTOBAUD
;
;******************************************************************************
;
;  Description:
;	Determine Baud Rate Of Serial Port By Timing Start Bit.  
;
;  Entry Requirements:
;	None
;
;  On Exit:
;	B/A Has Current Baud Rate (As 9600, 1900, etc For Displaying)
;	R0 Has Value For SMOD Bit Used
;	R1 Has Divisor Rate Used
;
;  Affected:
;	SCON, SBUF, TMOD, TH0, TL0, R0, R1, B, A, DPTR, PSW
;
;  Stack:
;	0 Bytes, Not Including Space Used By Called Routines
;
;  Comments:
;	The Tables Are Setup To Allow +-3% Variation In Timing.  If Can't 
;	Get A Good Baud Rate, Just Keep Trying.  The Routine Can And Will
;	Be Tricked If Not Running At 8/N/1.
;
AUTOBAUD	proc
		clr	es		; No Serial Interrupts
		clr	et0		; No Timer 0 Interrupt
		mov	scon,#052h	; Mode 3 Serial Port
		mov	tmod,#021h	; Timer 1 Mode 2, Timer 0 Mode 1
		mov	sbuf,#000h	; Send A Null For First Character
		setb	tr1		; Start Timer 1 Up
;
;  Wait For Start Bit, Run Timer While Start Bit High
;
l?p0:		clr	ri		; Ignore Any Character In SBUF
		clr	tr0		; Cancel Timer 0
		mov	th0,#000h	; Clear Timer 0 High
		mov	tl0,#000h	; Clear Timer 0 Low
		jb	p3.0,$		; Wait For Start Bit High
		setb	tr0		; Start Timer 0 Running
		jnb	p3.0,$		; Wait For Start Bit To Go Low
		clr	tr0		; Cancel Timer 0
;
;  Timer 0 Has Start Bit Period.  Test Against Table.
;
		mov	dptr,#Table	; Point To Table
l?p1:		mov	a,#0		; Set For MOVC
		movc	a,@a+dptr	; Get High Byte From Table
		cjne	a,th0,l?p2	; Compare
		mov	a,#1		; Set For MOVC
		movc	a,@a+dptr	; Get Low Byte From Table
		cjne	a,tl0,l?p2	; Compare
l?p2:		jc	l?p4		; If Greater, Try Next Entry
		mov	a,#2		; Set For MOVC
		movc	a,@a+dptr	; Get High Byte From Table
		cjne	a,th0,l?p3	; Compare
		mov	a,#3		; Set For MOVC
		movc	a,@a+dptr	; Get Low Byte From Table
		cjne	a,tl0,l?p3	; Compare
		setb	c		; Flip Status
l?p3:		jnc	l?p4		; If Less, Try Next Entry
;
		mov	a,#4		; Point To SMOD Status Byte
		movc	a,@a+dptr	; Get SMOD Byte
		mov	r0,a		; Move To R0 For Return
		mov	pcon,a		; Store It Back
		mov	a,#5		; Point To Speed Byte
		movc	a,@a+dptr	; Get Speed Byte
		mov	r1,a		; Move To R1 For Return
		mov	th1,a		; Setup Baud Rate Timer
		mov	tl1,a		; Setup Baud Rate Timer
		jnb	ri,$		; Wait For Character
		clr	ri		; Say Character Received Isn't There
		mov	a,#6		; Offset To Baud Rate High
		movc	a,@a+dptr	; Get High Of Baud Rate In Binary
		mov	b,a		; Store In B
		mov	a,#7		; Offset To Baud Rate Low
		movc	a,@a+dptr	; Get Low Of Baud Rate In Binary
		setb	es		; Allow Serial Interrupts
		ret			; Return To Caller
;
l?p4:		mov	a,#8		; Number Bytes In Record
		add	a,dpl		; Add In DPL
		mov	dpl,a		; Back To DPL
		jnc	l?p5		; If No Carry, Skip
		inc	dph		; Increment High Of DPTR
l?p5:		clr	a		; Clear For MOVC
		movc	a,@a+dptr	; Get Byte
		cjne	a,#-1,l?p1	; While Not -1, Loop
		sjmp	l?p0		; Try Again
;
;  All Values Calculated For 11.059200Mhz
;
Table:		dw	6328, 5960, 00040h, 00150; 150
		dw	3164, 2980, 000a0h, 00300; 300
		dw	2109, 1987, 000c0h, 00450; 450
		dw	1582, 1490, 000d0h, 00600; 600
		dw	0791, 0745, 000e8h, 01200; 1200
		dw	0527, 0497, 000f0h, 01800; 1800
		dw	0396, 0372, 000f4h, 02400; 2400
		dw	0264, 0248, 000f8h, 03600; 3600
		dw	0198, 0186, 000fah, 04800; 4800
		dw	0132, 0124, 000fch, 07200; 7200
		dw	0099, 0093, 000fdh, 09600; 9600
		dw	0066, 0062, 000feh, 14400; 14400
		dw	0049, 0047, 080fdh, 19200; 19200
		dw	-1
		endproc
;
;****************************************************************************
;
		end