Monitor for iSBC 8024 - test-drb@ccmp.vtda.org

4 Nov 2000

From: Richard Erlacher &lt;richard(a)idcomm.com&gt;

...
 That's interesting!  I was comparing the quoted
sizes of a couple of HDL
versions available on the web.  The smalles 650x I found was about 3200
gates, while the smallest Z80 was listed at 9200.  It's difficult to say 

This is true.  It is a larger cpu.

...
 Eric Smith reminded me some weeks back that the Z80 has
two complete
register sets, which pretty quickly leads me to conclude it's justified in

To be exact the z80 has

    A      A'        8BIT
    BC    BC'    16BIT
    DE    DE'    16BIT
    HL     HL'     16BIT
    IX                16BIT
    IY                16BIT
    SP              16BIT
    F    F'          ~8BIT FLAGS
    PC              16BIT
    I                  8BIT (HIGH 8BITS OF INTERUPT VECTOR)
    R                8BITS (REFRESH ADDRESS)

6502
     A              8BIT
    X               8BIT
    Y               8BIT
    PC            16BIT
    SP            9BIT  (HIGH BIT =1)
    STATUS    8BIT

Big difference in the number of bits for storage alone.  It accounts for
most of the
die area (ram/registers that is).

...
 consuming considerably more resources in an array than
the 650x core. One
...
 might conclude that the 8080 should lie between the
two, since it has more
...
 registers than the 650x, yet fewer than the Z80.  The
transistor count is
...
 not quite reflective of the register resources, but it
does appear that the
...
 8080 has more transistors used than the 650x. 

8080 is not near as efficient in logic usage as z80.

The different is in memory vs register usage in programming.  A
reasonably
complex 6502 program will always use more ram than similar in z80 if only
due to need for multiple pointers, local storage and parameter passing.

A while back I said I passed on an cmos ASIC project that was going to
use 8088 (actually 80186 core) as a embedded app. the client insisted
on it and planned to inegrate 32-64k of rom and at least 4-16k of ram
with
it. Application, remotely read peaking power meter.  People do this!

Compared to the 80186 core the z80 is tiny!

Allison