[sdiy] TB-303 cpu question - impossible

[Robin Whittle]

The TB-303 is a mask programmed 4 bit NEC CPU.  There are no such CPUs
available, including as far as I know any such CPUs with external ROM.
I don't think there could have been an external ROM version, because it
would take most of the pins to access the ROM.  Other than a special
device for development, I doubt if NEC ever made a chip with all the
extra pins required for operation with an external ROM.

There is no way anyone knows of reading the ROM.  Probably there is a
way of doing so as part of NEC's test procedure.

So no-one has the object code.  The CPUs are not available in any form.
 Other CPUs in devices such as TR-606s have different ROM data.

Its my impression that a lot of talk about this subject is not based in
reality, but on optimistic hopes that what happens in completely
different situations might somehow apply to the TB-303 CPU.

It is technically possible to analyse the operation of the CPU and to
create a new PCB to take its place, with some chip like a PIC programmed
to emulate its functions.  That would be a huge project.  For the actual
demand for CPU chips, which I guess in 12,000 or so TB-303s in
existence, are failing at about one a week somewhere in the world - it
is probably a lot easier to either write off the TB-303, buy another
TB-303 and grab its CPU, or forget about the sequencer and have a MIDI
In system installed.

I have installed the Devil Fish mods, with MIDI In for a TB-303 without
a CPU.

   - Robin

    http://www.firstpr.com.au/rwi/dfish/