Building the MSX-Audio BIOS upgrade for Music Module

Master (154)

01-05-2005, 16:52

I played with tthe MM to audio conversion a bit today. I NEED HELP!!

Should 74ls139 pin 8 be grounded? (YES)

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)
It did not work
Running SUPPER-X I found the sram mapped & mirrored to
0000,2000,4000,6000,8000,A000.
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
Call Audio still does not work.

I know the mirroring of the eprom can be due to the mappertype and super-x
readig it unmapped

What is wrong??

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By legacy

Hero (570)

01-05-2005, 21:32

It seems that I have the same scheme , and the difference is that this scheme used a 6164 instead of a 61256 and the pins you'r mention are switched.
If you want, i can send you that scheme .

By jpgrobler

Master (154)

02-05-2005, 07:13

Found the error

The schematic is correct except: (download date 29/4/2005 I add the date because the schema might be updated!)
pin 26 of the 27c256 (A13) should be insterted into the eprom socket! (wrong in schema)
pin 26 of the 27c256 (A13) should also be connected to 74ls139 pin 3 ( Correct in schema)

Ground 74ls139 pin8 also