Date   : Fri, 26 Nov 2010 15:14:29 +1100
From   : awilliams@... (Alan Williams)
Subject: Electron Ferranti ULA reverse engineering progress

Having looked at the output years ago on an oscilloscope I suspect a 2
bit D/A converter is used to generate the output waveform.  I couldn't
speculate on the in put though.
Alan

-----Original Message-----
From: bbc-micro-bounces+awilliams=linkme.com.au@...
[mailto:bbc-micro-bounces+awilliams=linkme.com.au@...] On
Behalf Of J.G.Harston
Sent: Friday, 26 November 2010 1:34 PM
To: bbc-micro@...
Subject: Re: [BBC-Micro] Electron Ferranti ULA reverse engineering
progress

James McGill wrote:
> I don't suppose you know of any resources for the BBC's 1200 baud 
> cassette interface? My best guess is that the analog cassette signal 
> is quantized to a digital signal and then processed in software

It's all processed in hardware, the software meerly reads/writes to the
6850 ACIA. The signals to/from the ACIA are converted to/from cassette
signals by the serial ULA.

See the circuit diagram here:
http://mdfs.net/Info/Comp/BBC/Circuits/bbc.gif

--
J.G.Harston - jgh@...     


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