For lab 03, we were supposed to create a basic game or calculator using 6502 assembly language.
My idea
We the professor noticed us, Assembly language is hard, and we should keep it simple as much as we can.
My idea was to create a simple calculator that would divide any number from 0 to 9 by 2 using LSR(Logical Shift Right).
The way it works
First I display a message to the user:
Type a number from 0 to 9:
I did it using dcb and CHROUT, this way:
LDY #$00
nextchar: ;DISPLAY INITIAL MESSAGE
LDA msg,Y
BEQ getnumber
JSR CHROUT
INY
BNE nextchar
msg:
dcb "T","y","p","e",32,"a",32,"n","u","m","b","e","r",32,"f","r","o","m",32,"0",32,"t","o",32,"9",":",0
Then I get the input from the user using CHRIN:
getnumber: ; ACCEPT ONLY NUMBERS
LDY #$00
JSR CHRIN
CMP #$00
BEQ getnumber
CMP #$30
BMI getnumber
CMP #$39
BPL getnumber
LDX A ;Load x register with A
JSR CHROUT
This code means accept only numbers from 0 to 9, if user enters something different than that then it will be ignored.
After that I display the following message:
Your number dividev by to is:
dividemsg: ;DISPLAY DIVIDE MESSAGE
LDA msg2,y
BEQ result
JSR CHROUT
INY
BNE dividemsg
msg2:
dcb $0d,"Y","o","u","r",32,"n","u","m","b","e","r",32,"d","i","v","i","d","e","d",32,"b","y",32,"2",32,"i","s",":",0
After the message is displayed the result should be outputs in the result label:
result: ; GET THE RESULT - LSR DIVIDE BY 2
LDY #$00
CPX #$00 ;Compare X with 0
BEQ zero ;Display divide by 0 message
LSR X ;Divide by 2
LDA X ; load result in A
JSR CHROUT ;Display the result
It is important to say that I could not make this part work properly, the result is not displaying to the user.
And if the user is trying to divide by 0, then a message should be displayed:
zero: ;MESSAGE IN CASE DIVIDING BY 0
LDA msg3,y
BEQ done
JSR CHROUT
INY
BNE zero
done: BRK
The entire code can be found here:
define SCINIT $ff81 ; initialize/clear screen
define CHRIN $ffcf ; input character from keyboard
define CHROUT $ffd2 ; output character to screen
define SCREEN $ffed ; get screen size
define PLOT $fff0 ; get/set cursor coordinates
LDY #$00
nextchar: ;DISPLAY INITIAL MESSAGE
LDA msg,Y
BEQ getnumber
JSR CHROUT
INY
BNE nextchar
getnumber: ; ACCEPT ONLY NUMBERS
LDY #$00
JSR CHRIN
CMP #$00
BEQ getnumber
CMP #$30
BMI getnumber
CMP #$39
BPL getnumber
LDX A ;Load x register with A
JSR CHROUT
LDY #$00
dividemsg: ;DISPLAY DIVIDE MESSAGE
LDA msg2,y
BEQ result
JSR CHROUT
INY
BNE dividemsg
result: ; GET THE RESULT - LSR DIVIDE BY 2
LDY #$00
CPX #$00 ;Compare X with 0
BEQ zero ;Display divide by 0 message
LSR X ;Divide by 2
LDA X ; load result in A
JSR CHROUT ;Display the result
zero: ;MESSAGE IN CASE DIVIDING BY 0
LDA msg3,y
BEQ done
JSR CHROUT
INY
BNE zero
done: BRK
msg:
dcb "T","y","p","e",32,"a",32,"n","u","m","b","e","r",32,"f","r","o","m",32,"0",32,"t","o",32,"9",":",0
msg2:
dcb $0d,"Y","o","u","r",32,"n","u","m","b","e","r",32,"d","i","v","i","d","e","d",32,"b","y",32,"2",32,"i","s",":",0
msg3:
dcb 32,"C","a","n","n","o","t",32,"d","i","v","i","d","e",32,"0","!",0
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