' Port 80 project.  By E. Negus  June 20, 2000
' 
' This project is used to help diagnose problems with
' IBM compatible motherboards by displaying the
' results of the Power On Self Test via the Port 80
' diagnostic port, in english, using a 2 Line x 40 
' character LCD display.  An EPROM is used for holding
' this data, which can be simply what is being tested
' or even the component locations of the components
' being tested.
'
' Program Operation:
'
' Get 2 chars from an EPROM, one nibble at a time via a
' `257 or `157 data selector.  Display on LCD and advance
' the CD4040 address counter for the next character. If
' the same post code is displayed for three seconds, write
' the entire text to the LCD display, if not, clear the
' CD4040 counter and home the display cursor to display
' the next code.  Also outputs short codes to a serial port
' which can be used to determine if an alternate branch
' is taken by the BIOS during POST.

' Plenty of space for additional instructions (also 16 chars
' on the LCD aren't in use!)


Symbol  E       =       5       ' Enable pin, 1 = enabled
Symbol  RS      =       4       ' Register select pin, 0 = instruction
				' + clears the CD4040, 1 = text
Symbol  AB      =       7	' Doubles as Serial output
Symbol  clk     =       6       ' Increments CD4040
Symbol	lsc	=	w0	' temp holding word
Symbol  lcs	=	w4	' temp holding word
Symbol	nsub	=	b2	' used to build character to display
Symbol  cnt     =       b3	' counter
Symbol  temb    =       b4	' temp holding byte
Symbol  char    =       b5	' character to display
Symbol	last	=	b6	' temp holding byte
Symbol	bnt	=	b7	' timing byte

' Set up the Stamp's I/O lines and initialize the LCD. 

begin:	let pins = %00000000	'Clear the output lines
	let dirs = %01111111	'One input, 7 outputs. 
	pause 100		'Wait 100 ms for LCD to reset. 
i_LCD:	let pins = %00000011	'Set to 8-bit operation. 
	pulsout E,1		'Send data three times
	pause 10		'to initialize LCD. 
	pulsout E,1		
	pause 10		
	pulsout E,1		
	pause 10		
	let pins = %00000010	'Set to 4-bit operation. 
	pulsout E,1		'Send above data three times.
        pulsout E,1
	let pins = %00001000
        pulsout E,1
	let char = 14		'Set up LCD in accordance with
	gosub wr_LCD		'Hitachi instruction manual. 
	let char = 6		'Turn on cursor and enable
	gosub wr_LCD		'left-to-right printing. 
	let char = 1		'Clear the display. 
	gosub wr_LCD
	high	RS		'Prepare to send characters. 

' LCD is setup.  Now display Port80 text.

loop:   for cnt=0 to 1		'Get & display first two characters
		gosub getdat
	next cnt
	let lcs = last * 256 + nsub
	if lsc = lcs then cbnt	'if same as last, check for how long
	serout ab,n2400,(nsub,last,10,13)	'if unique send it out
	let lsc = lcs		'for comparing later

clbnt:	let bnt = 0		'Clear timing variable
svbnt:	low     RS              'Home the LCD cursor , clear CD4040
        let char = 2
        gosub wr_LCD
	high rs
	goto loop

cbnt:	let bnt = bnt + 1
	if bnt < 60 then svbnt	'if same code for > 3 sec, display all text
	for cnt = 2 to 63
		gosub getdat
	next cnt
	goto clbnt

' Get character from `257 and display it on LCD

getdat:	let dirs = %11110000            'Set up I/O directions. 
	let pins = %00010000
	let last = nsub
	low ab
        let nsub = pins & %00001111     'Take low and high nibble
	high ab                         'readings from the 74HCT257
        let nsub = pins & %00001111 * 16 + nsub        
        pulsout clk,1			'Increment counter for next byte
        let char = nsub
	let pins = %00010000		'Keep RS High
	let dirs = %11111111		'All output pins.
	gosub wr_LCD			'write character to LCD
	return

' Write the ASCII character in char to the LCD. 

wr_LCD: let pins = pins & %00010000
        let temb = char / 16            'Put high nib of char into temb
        let pins = pins | temb          'OR the contents of char into pins 
        pulsout E,1                     'Blip enable pin
        let temb = char & %00001111     'Put low nib of char into temb 
        let pins = pins & %00010000     'Clear 4-bit data bus
        let pins = pins | temb          'OR the contents of temb into pins
        pulsout E,1                     'Blip enable pin
        return