RW    equ $08   * PB3 is R/W
RS    equ $04   * PB2 is RS
E     equ $02   * PB1 is E
PORTA equ $0000
PORTB equ $0001
PORTC equ  0x04
DDRA  equ $0002
DDRB  equ $0003
DDRC  equ  0x06
TCNT  equ $0084
TSCR  equ $0086       make bit7=1 to enable TCNT
Num1	equ $0800
Num1A equ $0801
Num2	equ $0802
Num2A	equ $0803
Num3  equ $0804
Num3A equ $0805
Ln1Cnt equ $0806
Ln2Cnt equ $0807
KeyHit equ $0808
equals equ $0809
ycount equ $0810
Math  equ  $0811	
Temp1  equ $0812
Temp2  equ $0813
Temp3  equ $0814
      org  $0819
buf   rmb  10  ; characters typed
cnt   rmb  1   ; loop counter, number of keys left to be typed


      org  $F000      Object code goes in ROM
***************LCDInit***********************
* Initialize HD44780 LCD display
* Inputs: none    Outputs: none
* Registers modified: A,CCR
LCDInit
      ldaa #$FF
      staa DDRA       Output to LCD data
      ldaa #$FF
      staa DDRB       Outputs pb1=E, pb2=RS, pb3=R/W
      clr  PORTB      E=0, RS=0, R/W=0
      rts

***************LCDOutChar***********************
* Output one character to HD44780 LCD display
* Inputs: RegA is ASCII character    Outputs: none
* Registers modified: B,CCR
LCDOutChar
      staa PORTA
      ldab #E+RS    E=1, RS=1, R/W=0
      stab PORTB
      ldab #RS      E=0, RS=1, R/W=0
      stab PORTB
      bsr  LCDWaitShort 40us wait
      rts

***************LCDOutCmd***********************
* Output command to HD44780 LCD display
* Inputs: RegA is LCD command    Outputs: none
* Registers modified: B,CCR
* Entry Mode Set 0,0,0,0,0,1,I/D,S
*     I/D=1 for increment cursor move direction
*        =0 for decrement cursor move direction
*     S  =1 for display shift
*        =0 for no display shift
*   Display On/Off Control 0,0,0,0,1,D,C,B
*     D  =1 for display on
*        =0 for display off
*     C  =1 for cursor on
*        =0 for cursor off
*     B  =1 for blink of cursor position character
*        =0 for no blink
*   Cursor/Display Shift  0,0,0,1,S/C,R/L,*,*
*     S/C=1 for display shift
*        =0 for cursor movement
*     R/L=1 for shift to left
*        =0 for shift to right
*   Function Set   0,0,1,DL,N,F,*,*
*     DL=1 for 8 bit
*       =0 for 4 bit
*     N =1 for 2 lines
*       =0 for 1 line
*     F =1 for 5 by 10 dots
*       =0 for 5 by 7 dots 
LCDOutCmd
      staa PORTA
      ldab #E      E=1, RS=0, R/W=0
      stab PORTB
      ldab #0      E=0, RS=0, R/W=0
      stab PORTB
      bsr  LCDWaitLong 1.54ms wait
      rts

***************LCDWaitShort***********************
* 20us wait HD44780 LCD display
* real display would require 37us
* Inputs: none Outputs: none
* Registers modified: B,CCR
LCDWaitShort
      ldd	#1
	*ldd  #360      8MHz
      addd TCNT      TCNT value at the end of the delay
sloop cpd  TCNT      EndT-TCNT<0 when EndT<Tcnt
      bpl  sloop
      rts

***************LCDWaitLong***********************
* 50us wait HD44780 LCD display
* real display would require 1.54ms
* Inputs: none Outputs: none
* Registers modified: B,CCR
LCDWaitLong
      ldd	#4
	*ldd  #12400    8MHz
      addd TCNT      TCNT value at the end of the delay
lloop cpd  TCNT      EndT-TCNT<0 when EndT<Tcnt
      bpl  lloop
      rts
******Initialize Keyboard*******
*Inputs: None
*Outputs: None
Key_Init movb #$00,DDRC
         movb #$00,PORTC
         rts
******Input from Keyboard*******
*waits for exactly one key to be pressed
*Inputs: none
*Outputs: RegA is ASCII code of key typed
Key_In   
   	  movb #$80,DDRC  ; activate row0
   	  ldaa PORTC
  	  anda #$0F
  	  cmpa #$07       ;"1" pressed?
  	  bne  not1
	  ldaa #$01
	  staa Num1
  	  ldaa #'1'
   	  jmp  found
not1 	  cmpa #$0B       ;"2" pressed?
     	  bne  not2
	  ldaa #$02
	  staa Num1
    	  ldaa #'2'
     	  jmp  found
not2 	  cmpa #$0D       ;"3" pressed?
     	  bne  not3
	  ldaa #$03
	  staa Num1
     	  ldaa #'3'
     	  jmp  found
not3 	  cmpa #$0E		;"+" pressed?
	  bne  notadd
	  ldaa #$2B
	  jmp  MathSym
notadd  movb #$40,DDRC  ; x0xxx activates row1
     	  ldaa PORTC
     	  anda #$0F
     	  cmpa #$07       ;"4" pressed?
     	  bne  not4
	  ldaa #$04
	  staa Num1
     	  ldaa #'4'
     	  jmp  found
not4 	  cmpa #$0B       ;"5" pressed?
     	  bne  not5
	  ldaa #$05
	  staa Num1
     	  ldaa #'5'
     	  jmp  found
not5 	  cmpa #$0D       ;"6" pressed?
     	  bne  not6
	  ldaa #$06
	  staa Num1
     	  ldaa #'6'
     	  jmp  found
not6 	  cmpa #$0E		;"-" pressed?
	  bne  notsub
	  ldaa #$2D
	  jmp  MathSym
notsub  movb #$20,DDRC  ; xx0x activates row2
     	  ldaa PORTC
     	  anda #$0F
     	  cmpa #$07       ;"7" pressed?
     	  bne  not7
	  ldaa #$07
	  staa Num1
     	  ldaa #'7'
     	  bra  found
not7 	  cmpa #$0B       ;"8" pressed?
     	  bne  not8
	  ldaa #$08
	  staa Num1
     	  ldaa #'8'
     	  bra  found
not8 	  cmpa #$0D       ;"9" pressed?
     	  bne  not9
	  ldaa #$09
	  staa Num1
     	  ldaa #'9'
     	  bra  found
not9 	  cmpa #$0E		;"*" pressed?
	  bne  notmult
	  ldaa #$2A
	  jmp  MathSym
notmult movb #$10,DDRC  ; xxx0 activates row3
     	  ldaa PORTC
     	  anda #$0F
	  cmpa #$07		;"c" pressed?
	  bne  notc
	  jsr  Clear
	  jmp  Key_In
notc	  cmpa #$0B       ;"0" pressed?
     	  bne  not0
	  ldaa #$00
	  staa Num1
     	  ldaa #'0'
     	  bra  found
not0 	  cmpa #$0D
	  bne  notequ
	  jsr  EquCmd
	  jmp  Key_In
notequ  cmpa #$0E		;"/" pressed?
	  bne  notdiv
	  ldaa #$2F
	  bra  MathSym
notdiv  jmp  Key_In     ; wait for exactly one
MathSym staa Math
	  ldy  #$00
	  movb Num1,Num3
	  ldaa #$01
	  jsr  LCDOutCmd
	  movb #$80,Ln1Cnt Sets counter line 1
        movb #$C0,Ln2Cnt Sets counter line 2
	  jmp  Key_In
found   staa KeyHit
	  jsr  LCDOutChar
	  iny
        rts
******wait for release
*inputs: none
*outputs: none
Key_Release
    	   movb #$F0,DDRC   ; activate all rows
wait     ldaa PORTC
    	   anda #$0E
    	   cmpa #$0E        ; none pressed?
    	   bne  wait
    	   rts

*Clears out display and variables*
Clear   
	  ldaa #$01
	  jsr  LCDOutCmd
	  clr  KeyHit
	  clr  Num1
	  clr  Num2
	  clr  Num3
	  movb #$80,Ln1Cnt Sets counter line 1
        movb #$C0,Ln2Cnt Sets counter line 2
	  rts
*End clear command.*

*Add Command.*
AddCmd
	  ldaa  Num1
	  adda  Num2
	  cmpa  #$FF
	  bgt   Error2
	  staa  Num1
	  rts
Error2  jsr   ErrorMsg
	  rts
*End of Add command.*

*Subtract command.*
SubCmd
	  ldaa Num1
	  suba Num2
	  cmpa #$00
	  blt  Error3
	  staa Num1
	  rts
Error3  jsr   ErrorMsg
	  rts
*End of Subtract command.*

*Multiply command.*
MultCmd
	  ldaa  Num1
	  ldab  Num2
	  mul
	  cmpb  #$FF
	  bgt   Error4
	  stab  Num1
	  rts
Error4  jsr   ErrorMsg
	  rts
*End of Multiply command.*

*Divide command.*
DivCmd
	  ldd   Num1
	  ldx   Num2
	  cpx   #$00
	  beq   Error5
	  idiv
	  xgdx
	  stab   Num1
	  rts
Error5  jsr   ErrorMsg
	  rts
*End of Divide command.*

*Outputs answer to the lcd screen.*
EquCmd
	  movb Num1,Num2
	  movb Num3,Num1
	  ldaa Math
	  cmpa #$2B
	  beq  Add
	  cmpa #$2D
	  beq  Sub
	  cmpa #$2A
	  beq  Mul
	  cmpa #$2F
	  beq  Div
	  rts  
Add	  jsr  AddCmd
	  jsr  Print
	  rts  
Sub	  jsr  SubCmd
	  jsr  Print 
	  rts  
Mul	  jsr  MultCmd
	  jsr  Print 
	  rts  
Div	  jsr  DivCmd
	  jsr  Print 
	  rts  
*End of Equales Ccmmand.*

*Prints answer to lcd*
Print	   
	   rts
*Finish Print command*

*Outputs Error message to lcd*
ErrorMsg 
	   movb #$80,Ln1Cnt Sets counter line 1
	   movb #$C0,Ln2Cnt Sets counter line 2
	   ldy  #ErrMsg
OutMsg   ldaa Ln1Cnt	 ; moves cursor back to 1st line
	   jsr  LCDOutCmd  ; Displays cursor on 1st line
	   ldaa 0,y
	   jsr  LCDOutChar
	   ldaa Ln2Cnt	 ; moves cursor to 2nd line 
	   jsr  LCDOutCmd  ; Displays cursor on 2nd line
	   ldaa 0,y
	   jsr  LCDOutChar
	   inc  Ln2Cnt	 ; Increments line 2 counter
	   inc  Ln1Cnt	 ; Increments line 1 counter
	   ldaa Ln1Cnt	 ; moves cursor back to 1st line
	   jsr  LCDOutCmd  ; Displays cursor on 1st line
	   iny
	   ldaa 0,y
	   cmpa #$00	   
	   bne  OutMsg
	   jsr  LCDWaitLong
	   jsr  Clear
	   rts
*End Error message command*


main 	   lds  #$0C00       stack grows down from $0BFF
     	   ldaa #$80
     	   staa TSCR         enable TCNT
     	   jsr  LCDInit
	
Loop	   ldaa #$01         clear
     	   jsr  LCDOutCmd
     	   ldaa #$38        N=1 two line,  F=0 5 by 7 dots      
     	   jsr  LCDOutCmd   DL=1 8-bit data
	   ldaa #$0E        set D=1, C=1, B=0
     	   jsr  LCDOutCmd   display on, cursor on, blink off
	   ldaa #$06        set I/D, S      
     	   jsr  LCDOutCmd   increment, no shift
	   lds  #$0c00
     	   ldx  #buf
     	   movb #10,cnt
    	   jsr  Key_Init
	   ldy  #$00
	   movb #$80,Ln1Cnt Sets counter line 1
	   movb #$C0,Ln2Cnt Sets counter line 2
scan	   jsr  Key_In
	   ldaa Ln2Cnt	 ; moves cursor to 2nd line 
	   jsr  LCDOutCmd  ; Displays cursor on 2nd line
	   ldaa KeyHit
	   jsr  LCDOutChar
	   inc  Ln2Cnt	 ; Increments line 2 counter
	   inc  Ln1Cnt	 ; Increments line 1 counter
	   ldaa Ln1Cnt	 ; moves cursor back to 1st line
	   jsr  LCDOutCmd  ; Displays cursor on 1st line
	   staa 1,x+       ; save
    	   dec  cnt        ; quit after 10
    	   beq  done
    	   jsr  Key_Release
    	   bra  scan
     
done 	   stop
     	   bra  Loop

ErrMsg   fcc  "Error"
	   fcb  0  

      org  $FFFE
      dc.w  main       Starting address after a RESET
      end