; Note: a 2 by 16 LCD is assumed

;****************** Constant Definitions ******************
symbol	control	= outpinsA		;control to AY and LCD (A.0-A.3)
symbol	BC1			=	A.0					;A.0 is BC1 on the AY chip
symbol	BDIR		=	A.1					;A.1 is BDIR on the AY chip
symbol  RS			= A.0  				;A.2 is the LCD RS line (Reg Sel)
symbol  Enable	= A.1  				;A.3 is the LCD E line (Enable)
symbol	bus			=	outpinsB		;main data bus to the AY chip (DA)

;time constants based on a 40 MHz clock
symbol	AYpulse		= 1					;AY write pulse width is 1uS
symbol	LCDpulse	=	10 				;LCD enable pulse width is 10uS
symbol	mSec			=	5					;one millisecond
symbol	secFifth	=	1000			;fifth of a second
symbol	secHalf		=	2500			;half of a second
symbol	secOne		=	5000			;one second
symbol	sec3			=	15000			;3 seconds

;AY-8910 control codes and register addresses
symbol	inactive	= %00000000	
symbol	latchData	= %00000010
symbol	latchAddr	= %00000011		
symbol	Reg7			=	%00000111	;Register 7 - data direction
symbol	Reg15			=	%00001111	;Register 15 - Port IOB
symbol	IOBOut		=	%10111111	;IOB data direction code	

;Here are various LCD commands which can be used.
symbol  clrHome = 1   ;clear the display, home the cursor
symbol  home    = 2   ;home the cursor only
symbol  RtoL    = 4   ;print characters right to left
symbol  insR    = 5   ;insert characters to right
symbol  LtoR    = 6   ;print characters left to right
symbol  insL    = 7   ;insert characters to left
symbol  lcdOff  = 8   ;LCD screen off
symbol  lcdOn   = 12  ;LCD screen on, no cursor
symbol  curOff  = 12  ;an alias for the above
symbol  block   = 13  ;LCD screen on, block cursor
symbol  under   = 14  ;LCD screen on, underline cursor
symbol  undblk  = 15  ;LCD screen on, blinking and underline cursor
symbol  left    = 16  ;cursor left
symbol  right   = 20  ;cursor right
symbol  panR    = 24  ;pan viewing window right
symbol  panL    = 28  ;pan viewing window left
symbol  mode1   = 32  ;one-line mode (4-bit data)
symbol  mode2   = 40  ;two-line mode (4-bit data)
symbol  bus4    = 32  ;4-bit data bus mode
symbol  bus8    = 48  ;8-bit data bus mode
symbol  line1   = 128 ;go to start of line 1
symbol  line2   = 192 ;go to start of line 2

;****************** Variable Definitions ******************
symbol  char    = b0  ;ASCII character to be displayed
symbol  cmd     = b0  ;an alias for the char byte
symbol  i       = b1  ;loop variable
symbol  j       = b2  ;and another one
symbol  row     = b3  ;offset into message table
symbol  index   = b4  ;pointer to current character

;*********************** Messages *************************
eeprom  0,  ("First we'll show")  ;0
eeprom  16, ("this message.   ")
eeprom  32, ("Then we'll blink")  ;2
eeprom  48, ("five times.     ")
eeprom  64, ("Now let's pan   ")  ;4
eeprom  80, ("left and right. ")
eeprom  96, ("Watch the line  ")  ;6
eeprom  112,("cursor move.    ")
eeprom  128,("A block cursor  ")  ;8
eeprom  144,("is available.   ")
eeprom  160,("Next we'll scroll this long message as a continuous ")
eeprom      ("marquee in one line mode. ")
eeprom  238,("Characters: ")
eeprom  250,("Bye!")

;********************** Main Program **********************
pgm:
 	setfreq em40							;40 MHz external resonator
  dirsA = %00001111					;A.0-A.3 are outputs
  dirsB = %11111111					;B.0-B.7 are outputs

	gosub init								;initialize AY and LCD display

	main:
		row = 0               	;print first message
	  gosub print
	  pause sec3            	;pause 3 seconds
	
	  row = 2               	;print next message
	  gosub print
	  pause sec3            	;pause 3 seconds  
	
	  for i = 1 to 5        	;blink it five times
	    cmd = lcdOff
	    gosub sendCmd
	    pause secHalf					;half-sec off
	
	    cmd = lcdOn
	    gosub sendCmd
	    pause secHalf					;then half-sec on
	  next i
	  pause secOne
	  
	;demonstrate panning
	
	  row = 4               	;print next message
	  gosub print
	  pause sec3            	;pause 3 seconds
	
	  for i = 1 to 16       	;pan left a step at a time
	    cmd = panL
	    gosub sendCmd
	    pause secHalf
	  next i
	
	  for i = 1 to 16       	;then pan right
	    cmd = panR
	    gosub sendCmd
	    pause secHalf
	  next i
	  pause secOne
	
	;demonstrate moving the cursor
	
	  row = 6               	;print next message
	  gosub print
	  pause sec3            	;pause 3 seconds
	
	  cmd = home							;home the cursor
	  gosub sendCmd
	
	  cmd = under           	;choose underline cursor
	  gosub sendCmd
	
	  for i = 0 to 15       	;move cursor across first line
	    cmd = line1+i
	    gosub sendCmd
	    pause secFifth
	  next i
	
	  for i = 0 to 15       	;move cursor across second line
	    cmd = line2+i
	    gosub sendCmd
	    pause secFifth
	  next i
	
	  for i = 15 to 0 step -1 ;move cursor back over second line
	    cmd = line2+i
	    gosub sendCmd
	    pause secFifth
	  next i
	
	  for i = 15 to 0 step -1	;move cursor back over first line
	    cmd = line1+i
	    gosub sendCmd
	    pause secFifth
	  next i
	  pause sec3
	
	;demonstrate blinking block cursor
	
	  row = 8									;print next message
	  gosub print
		
	  cmd = home           		;home the cursor
	  gosub sendCmd
	
	  cmd = block          		;choose blinking block cursor
	  gosub sendCmd
	  pause sec3							;pause 3 seconds
	  
	;demonstrate scrolling a lengthy one-line marquee
	
	  cmd = mode1           	;change to one long line mode
	  gosub sendCmd
	
	  cmd = clrHome						;clear screen, home cursor		
	  gosub sendCmd
	 
	  cmd = curOff          	;and disable it
	  gosub sendCmd
	  
	  for i = 160 to 237    	;print next message
	    read i, char
	    gosub sendChr
	  next i
	  pause secOne
	
	  cmd = home            	;home cursor once more
	  gosub sendCmd
	
	  for i = 0 to 141      	;scroll message twice
	    cmd = panR
	    gosub sendCmd
	    pause secHalf
	  next i
	  
	  pause sec3
		
	  cmd = clrHome         	;clear the screen
	  gosub sendCmd
	  
	  cmd = mode2           	;change back to two line mode
	  gosub sendCmd
		
	;demonstrate all of the characters
	
	  for i = 238 to 250    	;print next message
	    read i, char
	    gosub sendChr
	  next i
	
	  for i = 33 to 127     	;print first batch of ASCII characters
	    cmd = line1 + 12    	;overwrite each character displayed
	    gosub sendCmd
	
	    char = i
	    gosub sendChr
	    pause secHalf
	  next i
	
	  for i = 161 to 253    	;print next batch of ASCII characters
	    cmd = line1 + 12
	    gosub sendCmd
	
	    char = i
	    gosub sendChr
	    pause secHalf
	  next i
	
	;say good-bye
	
	  cmd = line2
	  gosub sendCmd
	
	  for i = 250 to 253    	;print last message
	    read i, char
	    gosub sendChr
	  next i
	  pause sec3
	goto main									;repeat in perpetuity
end

;************* Initialize AY and LCD on power-up *************
init:
  control = inactive				;clear BC1, BDIR, RS and Enable

  ;set up the AY Port IOB for output
  control = latchAddr				;latch address command
  bus = Reg7								;set address to register 7
  control = inactive
  bus = IOBOut							;make Port IOB output
  pulsout BDIR,AYpulse			;latch data
  
  control = latchAddr
  bus = Reg15								;address Port IOB
  control = inactive
  bus = 0										;clear Port IOB
  pulsout BDIR,AYPulse
  
  pause secFifth 						;let the LCD settle for 200 mSec
  
  cmd = bus8								;command for 8-bit operation
  gosub sendCmd
  pause 50									;pause 10 mS
  
  gosub sendCmd							;manufacturer recommends resends
  gosub sendCmd							;to allow for settling time
 
  cmd = bus4								;now make 4-bit mode
  gosub sendCmd
  gosub sendCmd							;again, redundancy here on purpose
  
  cmd = 0										;clear LCD inputs
  gosub sendCmd
  
  cmd = mode2								;two-line mode
  gosub sendCmd

  char = clrHome						;clear display, home the cursor
  gosub sendCmd

  char = curOff							;turn cursor off
  gosub sendCmd

  char = LtoR								;print left to right by default
  gosub sendCmd
return

;*************** Send a Character to the LCD **************
;To transmit a character, RS must be high.

sendChr:

  control = latchAddr			;latch the address
  bus = Reg15							;access Port IOB
  control = inactive
  bus = char >> 4			 		;shift high nibble right   
  pulsout BDIR,AYpulse		;latch data
  high rs
  pulsout enable,LCDpulse	;send it
  
  control = latchAddr			;latch the address
  bus = Reg15							;access Port IOB
  control = inactive
  bus = char & %00001111	;grab low nibble   
  pulsout BDIR,AYPulse		;latch data
	high rs
  pulsout enable,LCDpulse	;send it
return

;**************** Send a Command to the LCD ***************
;To transmit a command, RS must be low. It is by default..

sendCmd:
  control = latchAddr			;latch the address  
  bus = Reg15							;access Port IOB
  control = inactive
  bus = cmd >> 4			 		;shift high nibble right   
  pulsout BDIR,AYpulse		;latch data
  pulsout enable,LCDpulse	;send it

 	control = latchAddr			;latch the address  
  bus = Reg15							;access Port IOB
  control = inactive
  bus = cmd & %00001111		;grab low nibble   
  pulsout BDIR,AYpulse		;latch data
  pulsout enable,LCDpulse	;send it
return

;**************** Print a message to the LCD **************
;The variable 'row' points to the start of the string.

print:
  cmd = clrHome
  gosub sendCmd
  
  cmd = mode2
  gosub sendCmd
  
  cmd = line1           ;get set for first line
  gosub sendCmd

  for i = 0 to 15
    index = row*16+i
    read index, char    ;fetch next character and
    gosub sendChr       ;transmit to the LCD
  next i

  cmd = line2           ;get set for second line
  gosub sendCmd

  for i = 0 to 15
    index = row+1*16+i
    read index, char    ;fetch next character and
    gosub sendChr       ;transmit to the LCD
  next i
return