More thoughts on building a Z-80 (64bit!!!) - test-drb@ccmp.vtda.org

23 Oct 1998

Are z80's still being produced? If so, are they the same as the 1980
ones? I would think so, since the TI-86 (still in production) uses
a z80. BTW, I guess comparing the multi-Z80 system to a 386 isn't too
fair. How much faster is it than 1 z80 running the same program? Why
is everyone making multi-z80 machines, anyway? Why not 6502 or 6800
or even (gasp!) 8088?
...
 < 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

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