[sdiy] My New Project - PCSYNTH

[phillip m gallo]

-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Jaroslaw
Ziembicki
Sent: Tuesday, June 07, 2005 9:48 AM
To: SDIY; Rainer Buchty
Subject: Re: [sdiy] My New Project - PCSYNTH


----- Original Message -----
From: "Rainer Buchty" <rainer at buchty.net>
To: "Gorka Garcia" <torpedo at demadrid.com>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, June 07, 2005 4:05 PM
Subject: Re: [sdiy] My New Project - PCSYNTH


> ...which is not true for the ZX81 which is constantly feeding the pixel
> "pipeline" and is only able to do actual calculations during the
> vertical retrace. That's why it's so dog slow :)


That's right;  I can recall how long it took on the ZX81 to run a simple
Basic loop that displayed numbers 0,1,2,3,4,... It took approx.
ONE SECOND per number...

But the idea of using the Z80 microprocessor for video generating was
brilliant! As far as I recall, the Z80 jumped into the video memory
and "executed code", and the µP bus signals were used for video signal
generating.

Regards, Jarek

Yes, the ZX-80 or '81 would read a "NOP" instruction forced on the bus by
the "ULA" and each NOP instruction read generated the memory control
signalling for the Video Display.  I later used a technique similar to this
for micro based sampler.  I had the micro execute nonsense code which
generated bus signals which read an ADC, and loaded DRAM on "leading edge"
and output the converted data to a DAC on the trailing edge of code fetch.
This allowed 12 bit operations to occur without the interventin of the
micro.

regards,
p

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