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

[Roy J. Tellason]

On Tuesday 04 April 2006 04:08 am, Plutoniq9 wrote:
> 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......

I have NO idea if what I'm going to mention here applies to this specific 
model of equipment or not,  it's just something I bumped into once...

We were a Roland service center.  One time we were doing a "software upgrade" 
on some keyboard,  and the original part pulled was an EPROM,  the new 
replacement was a masked ROM.  And it didn't work.  After putting it in 
there,  the unit was completely dead.  So I called 'em...

(This was one of the real irritations about dealing with Roland,  no toll-free 
tech support,  and it took a while to get a tech on the phone,  and the info 
should've been sent out with the upgrade on a paper anyhow!)

What I was told was that I had to move two "jumpers" which actually consisted 
of two "zero-ohm resistors" that were surface-mount,  which sat right next to 
the part in question.  They were on one set of pads,  and I needed to move 
them to this other set of pads.

Maybe,  if you're lucky,  the board you're messing with has such an 
arrangement?

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
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