Re: Z80 / C128

From: Marko Mäkelä (
Date: 1998-04-28 23:13:38

On Tue, 28 Apr 1998 wrote:

> As we all (should) know, the C128 is equiped with an Z80 as well. I cannot 
> remember we ever discussed this CPU in one of our mails. Have there ever been 
> nice ideas regarding this processor?

Yeah, make it accelerate at 9.81 m/s², or try how high it jumps when given
220 volts. :-)  In the C128 the Z80 is quite crippled, since it runs at an
effective speed of approximately 2 MHz, which is like crawling.  The C128
is booted by the Z80, which quickly switches over to the 8502.  One thing
that is worth investigating is writing a program that runs simultaneously
on both processors.  The C128 Programmer's Reference Guide says that it is
illegal, undefined, forbidden or whatever to enable CP/M mode and C64 mode
simultaneously.  When I tested what happens if you do so, it seemed that
both processors were active on the bus simultaneously.  Writing a program
that would run on both chips is quite difficult, since the addresses from
the processors will be ANDed together all the time.  I would give it a try
if I had a detailed description of the Z80.

> I do remember a writing saying you can attach another 128 KB of memory
> to the expansion slot. If this is true, does anybody know some details? 

I think that this only refers to the C= 1700 RAM Expansion Unit, the same
thing that you can plug to a C64.  BTW, has anyone tried to connect the
REU to a VIC-20?


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