Re: Blast from the past... Z80!

On Jan 31, 11:58 pm, Jasen Betts <ja...@xxxxxxxxxx> wrote:
On 2009-01-31, Vladimir Vassilevsky <antispam_bo...@xxxxxxxxxxx> wrote:





MooseFET wrote:

On Jan 31, 4:10 am, Jan Panteltje <pNaonStpealm...@xxxxxxxxx> wrote:

Yes, I had one ZX80 and 2 ZX81.
The ZX81 integrated the Z80 TTL in one chip.
Very good BASIC too.

I had my ZX80 extended to 16K of RAM.  I had an FFT written for it and
code that made nice plots on the printer.  You could do quite a lot
with very little RAM in the ZX80.  The floating point basic of the
ZX81 took up more space for your program.  With a twice as big of a
EPROM chip and a switch a ZX80 could be made as a "multi-boot"
machine.

The ZX81 basic stored every number twice in the program.  One copy was
the text to be displayed and the other was the actual floating point
value.  As a result, with some poking, you could make a program that
appeared to say

10 LET A=1 + 1
20 PRINT A

and have it print 3

I built ZX Spectrum with 128k RAM and the floppy drive using the
discrete logic ICs on the CAMAC breadboard. At the time, that was far
better computer then what was offered by Russian industry :-)
Did quite a lot of real programming on it.
BTW, the Spectrum 48k ROM BASIC is a jewel of assembly programming; I
can see the hand of the distinguished master.

Speaking of Z80 architecture, it wasn't bad for C programming. I wonder
what it would take to make it pipelined 1 cycle per instruction, and how
it would compare to AVR/PIC18/HC11.

the mundane instructions weren't any more complex than the AVR ones

but, to get one instruction per cycle you'd need a harvard architecture.

things like LDI aren't going to work one-per-cycle.
as they go to ram twice

If you fetch more bytes per fetch operation than an instruction is
long, you could have an extra trip to RAM here and there, but
generally, I agree with you.

If you look at some DSP chips, they have more than just the two busses
of the Harvard machine.
.

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