[MSX] MSX-Audio BIOS upgrade for Music Module
schmidlin at gmail.com
Mon May 2 05:00:15 CEST 2005
> I have lots of w24m257 (32k) sram IC's
> How can they be used in this circuit?
I haven't tested this IC. After some googling it seems to be 61256
equivalent. Looking at the datasheet, theorically it can work.
> I played with tthe MM to audio conversion a bit today. I NEED HELP!!
Ok, let's see if I can help. :)
> Should 74ls139 pin 8 be grounded? (YES)
Yes, it MUST! The pin-8 of the 74ls139 is THE ground pin of this CI.
Sorry if I didn't let this clear on the documentation. The standard pins
GND and Vcc of all CIs must be conected for any circuit to work.
I'll revise that on the documentation to avoid confusion.
> I build it with a 32k sram grounding the 2 extra adresslines (what a waste,
> but I have them in ample supply old 286/386 motherboards)
You don't need to ground them, just conect to the respective pins on the
EPROM. The 74LS139 will do the chip-selection acordingly.
> It did not work
> Running SUPPER-X I found the sram mapped & mirrored to
> Sram is stable
> I could not read anything else (see the eprom)( 1000, 3000 etc is FF)
> I switched the CS (CE) signals!
> 27C256 pin 20 to 74LS139 pin 11
> 61256 pin 20 to 74LS139 pin 12
> Now Sram is mapped & Mirrored to 1000, 3000, 5000, 7000, 9000, B000
> Sram is stable
> I do read data on (0000,2000,8000, A000),(4000,6000) () mirrored inside
> the pair
There's something wrong here...
Where did you connected the pin-15 of the 74LS139? It must me connected
to the pin-20 of the eprom soquet on the MM. Please note that the pin-20
of both 27C256 and the SRAM must not be connected to this same pin, but
to the pins 12 ans 11 of the 74LS139, respectively.
Also check the A13 pin of your 27C257, as it may be connected to the
wrong place. Maybe its short-circuited somewhere? Are the A12 and A13
lines short-circuited? Because they must not be.
On the msxaudio-BIOS.gif file, the only lines short-circuited are the
"Y" like ones that have the same color. There are only two of them,
labeled "/CS Soquete (pin-20)" and "IC3, pin-1".
> Call Audio still does not work.
With all this extra-mirroring it will not work... Check carefully for
short-circuited signals. Start checking your A13 and A12 lines.
> I know the mirroring of the eprom can be due to the mappertype and super-x
> readig it unmapped
There's no mappertype, since it's 32KB plain ROM. The extra-mirroring is
being caused by some wrong wiring, probably. By doing the
quick-and-dirty method you should get the following layout:
0000h-2fffh = EPROM's respective address
3000h-3fffh = SRAM's respective address
4000h-6fffh = EPROM's respective address
7000h-7fffh = SRAM, mirror of 3000h-3fffh
8000h-afffh = EPROM, mirror of 0000h-2fffh (*1)
b000h-bfffh = SRAM, mirror of 3000h-3fffh (*1)
*1: This only happens on the quick-and-dirty method, and is ignored by
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