17 Dec
2001
17 Dec
'01
5:28 a.m.
Richard Erlacher wrote:
The 650x core is apparently known to be about 3300
gates, if you can go by their
putative gate count. However, you can check 'em out for yourself. Google will
turn up several. As you might expect, the Z80 core is quite a bit larger and
runs somewhat slower. I don't think anyone's done the 650x core
"right" yet,
because most of the HDL's still are too big.
Lets say 3K gates. Lets also define a small FPGA is one that fits in a
84 pin
PLCC. The FPGA is used just for the CPU - no ram , rom , or I/O devices.
Looking at free-6502 as a guide. http://www.free-ip.com/6502/
it is really hard to tell just how many CLB's are used, but are just
over the
limit of what fits in small FPGA is what it looks like.
I remember the trade (~1976-77) mag's telling us
that the 6502 was <1/4 the size
of the Z80 though they were in the same technology. The only way I can see that
happening, aside from the vastly reduced internal resources that the 650x has,
is a much slicker design.
I suspect this is because
1) All registers but the PC are 8 bit.
2) Instructions grouped into fewer internal states per clock.
I think a z80 instruction could have 17+ states where a
6502 used up to 5 states.
--
Ben Franchuk --- Pre-historic Cpu's --
www.jetnet.ab.ca/users/bfranchuk/index.html