Machine Code Problem

[mrtinb]

The numbers 0 - 9 on the ZX81 is character number 28 to 37. Thus if you have a number between 0 and 9, and add 28, you get the characters '0' to '9'.

[MrVertigo]

But to get the number to display as a decimal rather than a ZX81 character graphic, is it the ADD A, 28 line that is accomplishing that?

[MrVertigo]

Oops we’re out of step. Thanks for the detailed explanation. That’s great!

[dr beep]

First routine until the space-line

A holds number, HL holds position on screen

19A38E58-B8D2-4B12-85FF-9F993FC524B2.png

This is the shortened version I used in a later game

Code: Select all

	ld	hl,location-1
	ld	bc,#364				; 3 loops, 100 10 and units, 100 first
set0	inc	hl				; goto current position
	ld	(hl),27				; signal "-1"
setp	inc	(hl)				; add 1 to position
	sub	c				; take of 100 or 10
	jr	nc,setp				; continu sub
	add	a,c				; undo last change
	ld	c,10				; 10 is next position
	djnz	set0				; do 10 and 1, but 1 as 10
	add	a,(hl)				; 1 is shown as "0"
	ld	(hl),a				;  now show units

[1024MAK]

But to get the number to display as a decimal rather than a ZX81 character graphic, is it the ADD A, 28 line that is accomplishing that?

That’s what I was trying to demonstrate with the BASIC program in my earlier post…

But simply adding 28 only works if your number is a single digit. You have to deal with each digit individually.

Mark

[MrVertigo]

But to get the number to display as a decimal rather than a ZX81 character graphic, is it the ADD A, 28 line that is accomplishing that?

That’s what I was trying to demonstrate with the BASIC program in my earlier post…

But simply adding 28 only works if your number is a single digit. You have to deal with each digit individually.

Mark

Ah, I see what your basic program is doing now!

[MrVertigo]

First routine until the space-line

A holds number, HL holds position on screen

19A38E58-B8D2-4B12-85FF-9F993FC524B2.png

This is the shortened version I used in a later game

Code: Select all

	ld	hl,location-1
	ld	bc,#364				; 3 loops, 100 10 and units, 100 first
set0	inc	hl				; goto current position
	ld	(hl),27				; signal "-1"
setp	inc	(hl)				; add 1 to position
	sub	c				; take of 100 or 10
	jr	nc,setp				; continu sub
	add	a,c				; undo last change
	ld	c,10				; 10 is next position
	djnz	set0				; do 10 and 1, but 1 as 10
	add	a,(hl)				; 1 is shown as "0"
	ld	(hl),a				;  now show units

Nice!

[MrVertigo]

When you get down to this level of programming it makes it even more hilarious to hear some people say computers can become sentient.

[1024MAK]

When you get down to this level of programming it makes it even more hilarious to hear some people say computers can become sentient.

HAL 9000 disagrees

Mark

[MrVertigo]