More thoughts on building a Z-80 (64bit!!!)

From: Allison J Parent <allisonp_at_world.std.com>
Date: Fri Oct 23 15:28:37 1998

< Wire wrap?...hmmm I have problems with that in ohmic losses even the
< connections is good, soldering them helped a bit but no dice.

Huh? I have 6 cards, s100 protoboards with about 25-40 pieces of mos and
TTL on them that I wrapped in 1981 still running. Ohmic losses? What were
you doing wrong. Remember #30 is for signals not power!

< Have data transfers done with DMA, all memory mapped and irq driven
< to knock subCPU as needed to grab data then place it in CPU's lap.
< Leave CPU alone for processing. How about that?

Those 6 boards built a multi z80 system with DMA and slave processors for
things like IO and disks. It helps but the z80 bus is so busy that it's
very hard to slip inbetween cycles so you steal cpu cycles by holding it
off with BUSRQ/. Z280, z8000 and Z380 use burst mode access to the bus so
that other devices can get in and get a few cycles without holding up the
cpu. Even with slaves you reach a bottleneck between memory management
and overhead to move data around. Still the results with 6mhz z80s were
enough to blow away 386/16 class machine for text oriented applications.

Allison
Received on Fri Oct 23 1998 - 15:28:37 BST