Detecting NTSC/PAL VICs

brighty · Post by **brighty** » Fri Mar 20, 2009 10:22 pm

Hi All,

I'm sure I saw a mention in the forums some time ago about being able to detect a PAL vs NTSC VIC programatically, but for all my searches I can't find it again

Does anybody recall which memory location it is and the value it contains PAL vs NTSC?

nippur72 · Post by **nippur72** » Sat Mar 21, 2009 2:10 am

from the Software Sprite thread:

this address $EDE4 (NTSC=$05, PAL=$0C) [...],

brighty · Post by **brighty** » Sat Mar 21, 2009 3:37 am

nippur72 wrote:from the Software Sprite thread:
this address $EDE4 (NTSC=$05, PAL=$0C) [...],

Thanks! I thought I'd searched this thread, as that was where I recalled I'd seen it. Damn!

carlsson · Post by **carlsson** » Sat Mar 21, 2009 5:50 pm

Of course if some naughty fellow has replaced the Kernel ROM with one for the wrong machine, it won't work. On the other hand it means the VIC would boot up with an off-centered screen every time. But to this point it is the best/simplest way I can think of. One probably could wait for a certain raster line and set up a timer but it would be more work for the same benefit.

tlr · Post by **tlr** » Sun Mar 22, 2009 3:16 am

I thought I'd give an example of the raster line method, which as noted does not rely on the Kernal ROM.
This is the way it is implemented in victracker:
(must have interrupts disabled)

Code: Select all

;**************************************************************************
;*
;* CheckPAL
;* Returns:	 Acc=0 on NTSC-M systems, Acc!=0 on PAL-B systems
;*		 (and sets PAL_Flag accordingly)
;*
;******
CheckPAL:
; find raster line 2
	lda	#2/2
cp_lp1:
	cmp	$9004
	bne	cp_lp1
; now we know that we are past raster line 0, see if we find raster line 268
; before we find raster line 0
cp_lp2:	
	lda	$9004
	beq	cp_ex1
	cmp	#268/2		; This line does not exist on NTSC.
	bne	cp_lp2
cp_ex1:	
	sta	PAL_Flag
	rts

brighty · Post by **brighty** » Sun Mar 22, 2009 3:51 am

Thanks for all the replies. I've gone with the EDE4 method for now, less bytes and I'm not too bothered if my code wont run on custom kernals.

It seems to work fine when testing in VICE (NTSC and PAL) and on a real PAL VIC. I don't have access to an NTSC VIC to test. Would anybody be willing to test out a PRG for me to make sure that there is no flicker and the screen is visible? (It's a game in progress, no interaction yet, requires 8/16K expansion).

Thanks

a1bert · Post by **a1bert** » Tue Mar 24, 2009 2:00 pm

brighty wrote:I'm not too bothered if my code wont run on custom kernals.

Well, there are some machines around that have PAL ROM's but are NTSC-converted...

I used this in VIMM:

Code: Select all

	; detect the system
	lda #0
	sta SYSTEMSEL
0$	lda $9004
	cmp #1
	bne 0$		; wait for line 1
1$	lda $9004
	beq 2$		; line 0 reached -> NTSC
NTSC_LINES = 261
	cmp #NTSC_LINES/2+2
	bne 1$
	inc SYSTEMSEL
2$	; system detected: 0 for NTSC, 1 for PAL

amramsey · Post by **amramsey** » Tue Mar 24, 2009 4:11 pm

brighty wrote:Would anybody be willing to test out a PRG for me to make sure that there is no flicker and the screen is visible? (It's a game in progress, no interaction yet, requires 8/16K expansion).

I can do it. I've got an NTSC vic with memory expansion. Do you have a link to the file?

brighty · Post by **brighty** » Tue Mar 24, 2009 9:03 pm

amramsey wrote:I can do it. I've got an NTSC vic with memory expansion. Do you have a link to the file?

Thanks a million. The PRG can be found here

amramsey · Post by **amramsey** » Wed Mar 25, 2009 4:44 pm

Looks really good. The screen was centred, no flickering or any funny business. The only problem was that the score at the top was cut off (about half of it) on my TV screen. I tried it out on a 1080 monitor also and the score was completely missing.

There was perhaps enough room at the bottom of the screen for about 1/2 a level of blocks or so. When the baddies jump off the bottom they can be seen right until the plastic on the monitor (ie- no border at the bottom).

Loading on 1080 (to give you an idea of the normal borders on the vic)

Gameplay

15 second video (probably have to right click and save it):
http://aaronramsey.com/public/vic20/qbert.mpg

brighty · Post by **brighty** » Wed Mar 25, 2009 5:28 pm

amramsey wrote:Looks really good. The screen was centred, no flickering or any funny business.

First off, a big thanks for putting in the time and effort to help me out, I really appreciate it. I can only test the NTSC version on VICE and this really illustrates the necessity of testing on real hardware.

amramsey wrote:The only problem was that the score at the top was cut off (about half of it) on my TV screen. I tried it out on a 1080 monitor also and the score was completely missing.

There was perhaps enough room at the bottom of the screen for about 1/2 a level of blocks or so. When the baddies jump off the bottom they can be seen right until the plastic on the monitor (ie- no border at the bottom).

I suspected I was pushing the display borders a bit on NTSC trying to display 28 rows. I think I can get away with trimming the top row off and moving the score down. I'll have a play with this over the weekend. I'll add keyboard input for screen centering too (horizontal & vertical), to allow for any differences between TVs and monitors.

Once again, thanks a million for the work you put in, especially with the video and pictures, they truly do speak a 1,000 words.

brighty · Post by **brighty** » Wed Mar 25, 2009 5:32 pm

a1bert wrote:
brighty wrote:I'm not too bothered if my code wont run on custom kernals.
Well, there are some machines around that have PAL ROM's but are NTSC-converted...

Ah, I didn't know people swapped ROMs like that

I'll change the detection code over the weekend to use a1bert/tlr's method.

Thanks to both of you for the code and info. My credits list is growing already

a1bert · Post by **a1bert** » Thu Mar 26, 2009 3:02 pm

brighty wrote:Ah, I didn't know people swapped ROMs like that

Actually it's the other way around: the ROM's are original, but the video chip has been changed. See http://www.iki.fi/a1bert/Dev/PAL2NTSC.html