tr-909 schem's

[Fraser, Colin J]

> -----Original Message-----
> From: WeAreAs1 at aol.com [mailto:WeAreAs1 at aol.com]
> Sent: Saturday, October 28, 2000 12:35 PM
> To: alan.p at clear.net.nz; synth-diy at node12b53.a2000.nl; Fraser, Colin J
> Subject: Re: tr-909 schem's
> 
> << I figure that the
> HN61256P-C4x is the eproms containing the sample data for 
> hihat, crash, and
> ride. Is that right? >>
> 
> Mmmm... HN61256 sounds more like a part number for a Hitachi 
> static RAM chip, 
> in which case it would be for storing the 909's pattern and 
> song data.  I 
> don't have the schematics handy, so I'm not sure.  I'll bet 
> that Colin Fraser 
> knows... Colin?

The 61256s are mask programmed ROMs.

You can use 27256 EPROMs in place of them in a clone, bearing in mind a
couple of necessary changes.

Roland, for reasons known only to themselves, chose to invert the sense of
pin 22, Chip Enable, for the Hi-Hat samples.
On the Hi-Hat ROM pin 22 is active HIGH.
On the Crash and Ride roms, the pin is active LOW (as usual).

The way round this is to use the NOT Q output on the 4013 that drives the Hi
Hat CE line.
You'll see that the NOT Q output is used for CE on the other 2 ROMs. 

Also, pins 20 & 26 need to be swapped. On the Roland ROMs, pin 20 is a Chip
Select line, and pin 26 an address line.
This is different to a standard 32k eprom.

The address and data lines on the Roland ROMs are also jumbled up. They
don't follow the standard pin numbering conventions for EPROMs.
I didn't bother working out the counter bit to address pin mapping. Instead
I just extracted the data byte by byte and used the nominal address lines
for my clone.
I only had to work out which bits were which on the data lines.

I've got some half finished single sided PCB layouts for the 909 sampled
sounds I need to find time to complete.
When I'm done, I'll post these on my web page along with HEX files of EPROMs
that are guaranteed to work with the PCBs without any of the hacking that I
had to do ;-)


Colin f