Date   : Thu, 16 Apr 2009 11:49:42 +0100
From   : philpem@... (Philip Pemberton)
Subject: ReCo6502 now available

Phill Harvey-Smith wrote:
 > Dual port ram with CPLD controling springs to mind.

Not exactly cheap though. ?5.29 from Farnell for a 1Kx8 dual-port RAM (Cypress 
CY7C131), plus about ?3 for a CPLD (Altera MAX3064A, 64 macrocells). You could 
use a couple of FIFO chips instead (IDT 7201 -- 512x9), which clocks in at 
?4.72. Still not particularly cheap though, but easier than the dual-port RAM 
(which would involve the use of rather a lot of I/O pins on the CPLD to drive 
the RAM).

The FPGA route is interesting, though. An Altera EP2C5Q208 (Cyclone II, 5000 
LEs, 142 I/O pins, 208 pin QFP package) would probably suit, and they can be 
sourced for around ?11 plus VAT. Level translators (e.g. 74LVC245 or similar) 
cost about a quid each, and you'll probably only need three or four of them 
(one or two for the 6502 bus, same again for the outputs).

?35 each is probably about right.

 > The real pain with CPLDs is that it seems as the number of logic blocks 
goes up so does the number of pins,

The same applies to FPGAs, although when they go up in size, they tend to end 
up in nasty leadless SMD packages as well.

 > Believe me soldering a 100 pin package with 0.5mm pins is
 > no fun at all :(

You'll *really* enjoy soldering BGA256es then :)

-- 
Phil.
philpem@...          
http://www.philpem.me.uk/