Philips MSX2 differences?

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By esau

Rookie (19)

esau's picture

04-04-2009, 13:19

Hi!

We've just finished a demo for unexpanded MSX2, to be released shortly.
But there are some strange problems: The demo is developed using
a Philips NMS8280, and works perfectly on that machine, however when
tested on NMS8250 and NMS8245 there are some bugs. Do the
superimpose features of the 8280 affect the performance of the VDP in
any way? Does it have a different clock frequency than standard MSX2?
As far as i understand they should be identical, or is my machine faulty?

Any help appreciated, we're kind of in a hurry here!

regards
esau / traktor

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By Jipe

Paragon (1500)

Jipe's picture

04-04-2009, 13:43

in 8280 the VDP clock is not with the same oscillator but i don't know if affect performance ?

By PingPong

Prophet (3756)

PingPong's picture

04-04-2009, 16:08

Maybe it affect sync between z80 and vdp itself. With one clock oscillator there is some sort of sync between vdp and z80. Normally z80 clock is given by vdp itself.
If you are writing time sensitive demo there is a chance that things does not goes so well....TongueTongue

By hap

Paragon (2037)

hap's picture

04-04-2009, 16:21

PingPong may be right, if this small test shows a wild diagonal effect, you shouldn't assume that every line is exactly 228 Z80 cycles:

10 data f3,db,99,00,00,00,00,3e,1e,d3,99,00,00,00,00,3e,87,d3,99,29,29,00,00
15 data 00,00,00,00,3e,11,d3,99,00,00,00,00,3e,87,d3,99,29,c3,2b,d0,c3,03,d0
20 clear200,&hd000:definta-z:b=&hd000:restore10:fori=bto(b+45):reada$
25 pokei,val("&h"+a$):next:defusr0=b:x=usr0(0)
org $100
; exactly 228 clocks per line?
; simple version

di
in a,($99)

; 228 total
loop:

; 80
; grijs
nop		; 5
nop		; 5
nop		; 5
nop		; 5
ld a,$1e	; 8
out ($99),a	; 12
nop		; 5
nop		; 5
nop		; 5
nop		; 5
ld a,$87	; 8
out ($99),a	; 12

; 36
add hl,hl	; 12
add hl,hl	; 12
nop		; 5
nop		; 5

; 80
; zwart
nop		; 5
nop		; 5
nop		; 5
nop		; 5
ld a,$11	; 8
out ($99),a	; 12
nop		; 5
nop		; 5
nop		; 5
nop		; 5
ld a,$87	; 8
out ($99),a	; 12

; 34
add hl,hl	; 12
jp nextlabel	; 11
nextlabel:
jp loop		; 11

By Edwin

Paragon (1182)

Edwin's picture

04-04-2009, 17:52

According to the v9938 handbook, horizontal timing is changed from 1368 vdp cycles to 1365 vdp cycles when an external source is selected (bit 4/5 of R#9).

By esau

Rookie (19)

esau's picture

04-04-2009, 22:23

Thanks a lot guys! This might be the answer to our troubles, a "wild diagonal effect" is exactly what we're fighting here Smile

By esau

Rookie (19)

esau's picture

05-04-2009, 18:51

There, problem solved. It seems indeed that the NMS8280 has a different VDP clock. So, am I right in assuming the the 8280 is the odd one and most other MSX2's have the same VDP clock?

By hap

Paragon (2037)

hap's picture

05-04-2009, 19:16

Good! Smile
No, don't assume that the 8280 is the only one, this quirk hasn't been researched well yet. What about Edwin's remark?

*edit*and most other MSX2's have the same VDP clock?This is true though.
The 's' is a strikeout bbcode that's unsupported by this forum Tongue

By Jorito

Mr. Ambassadors (1767)

Jorito's picture

05-04-2009, 19:28

The 's' is a strikeout bbcode that's unsupported by this forum Tongue
No, it's not Tongue

By PingPong

Prophet (3756)

PingPong's picture

05-04-2009, 20:06

There, problem solved. It seems indeed that the NMS8280 has a different VDP clock. So, am I right in assuming the the 8280 is the odd one and most other MSX2's have the same VDP clock?
Hey can we get the screenshot of the demo?

By esau

Rookie (19)

esau's picture

05-04-2009, 20:15

You'll all see the demo once it's released Smile Have patience and thanks again!

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