[sdiy] Roland Mask ROM's (i.e 707, 909) read/write

[Plutoniq9]

Hi,

Hope the subject line was informative enough!

I'm working on a project to find a way to create/use standard 27c256 eprom's 
or modern flash ROM's in the Roland TR-707 & 727 machines. However, this has 
not been a necessarily easy road up to now, which is why I thought I'd come 
to the list to see if anyone might be able to help. Once I am able to read 
the ROM's, then I can figure out how to go about creating a replacement 
soundset(s).

Some of the problems the Roland mask ROM's (HD61256P) present;

-Address-lines are mixed up from jadec standard. My present meathod or 
re-ordering the address-pins so my eprom programmer can read them is by 
breadboarding the Roland ROM and running wires to the correct locations on 
my programmer (messy & 28 of 'em, but solves the problem).

-Roland's CS (chip select) is pin 26 while pin 20 is an address pin. These 
need to be swapped to match 27c256 standard pinout. (Fix as above)

-The final problem, and most frustrating, is that pin 22 (Output-enable or 
chip-enable) actually needs to be clocked in order for the data pins to 
output data, you can't just tie it high or low. When the pulse goes high (on 
every pulse), out comes the data.

The last issue is where I'm stuck. In the 909 or certain 707 ROM's, Pin 22 
(OE) is pulsed by the same clock that drives the address counters. However, 
in a normal eprom programmer, this pin is normally just taken low.....How am 
i supposed to clock this line and have it in sync with my address counter in 
the my programmer? I'm stumped, Roland sure made it difficult......

Any ideas?

Thanks

Ryan