16 Jun
2008
16 Jun
'08
7:04 p.m.
On Monday 16 June 2008 21:53, bfranchuk at jetnet.ab.ca wrote:
Roy J. Tellason wrote:
Thanks.
I'm thinking about building a z80 board,
with varying amounts of "stuff"
attached, with RAM and ROM that may be NMOS or CMOS, and some
indeterminate number of Z80-family and compatible peripheral chips.
My question is this: At what point do you _need_ to have address and
data bus buffer chips?
Read the $%#! manual to put it bluntly. A simple guess is once your design is larger than a
small card,
Define "small".
you need I/O buffering. I think a 6800 cpu can drive
about 150 pf and a
typical load is 10 pf at rated speeds.
I'm not familiar with many 6800 designs, but I was somewhat surprised to see
how limited some parts are, like the 8085 in the "8085 Cookbook" where you
could really get away with very little. OTOH, the c64 doesn't use any
buffering _at all_ and yet the CPU in there seems to have little trouble
driving 3 ROM chips, a set of 8 4164s, plus all the peripherals. I'm
guessing that the Z80 is probably somewhere in between, and that the
datasheet probalby won't give me the whole story anyhow.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin