Date   : Tue, 26 Oct 2010 11:34:42 +0100
From   : afra@... (Phill Harvey-Smith)
Subject: Reversing the Tube ULA (destructively)

Mark Haysman wrote:
> Well you've been in the discussion on the *. forums and seen the 6502 
> Internal Co-Pro I've done for the M128, which uses a Xilinx XC3S50AN. That 

Indeed :)

> chip doesn't need an external config prom, as it has it built in. The level 

It doesn't ohh that's cool, humm I might see if that's also a feature of 
the version that has less pins.....I know I can mount the tqfp 100 
packages on self made boards, not sure about the higher pin count.

> shifters are a pain in the butt, and seem to operate most illogically! I'm 
> currently using a 74LVC16T245, which is designed so that either side of the 
> buffer can operate at any voltage (between 2.5 and 5), however, operating 
> the Beeb side at 5v just causes garbage on the screen, it seems happier 
> running it at 3.3v?

Which is odd indeed though I think that a 3.3V high is within the range 
that LSTTL and HC sees as on, so it should work, but what is puzzling is 
that the 5V setting doesn't :(

>> I just wish someone did a CPLD with lots of logic but not using stupid
>> numbers of pins :(
> 
> I'd prefer a 5v FPGA in a 40 pin DIP package with the internal logic of an 
> XC3S200AN! Bliss!

Yeah that would be nice, I'd settle for PLCC too, at least those are 
also socketable :)

> Have to agree that an "exact" clone would be preferable. I'm working with Ed 
> and Richard on his open source tube code to try and get it 100%, but there 
> seem to be odd quirks in there that would be a lot easier to solve if Ed 
> could have success with a proper RE of the original chip.

Indeed if you know exactly how the original worked then copying it 
becomes much less difficult, as you don't have to try and guess how it 
works.

Cheers.

Phill.