Re: CD's, C64's and error-correction

From: Marko Mäkelä (
Date: 1999-10-08 10:54:06

On Fri, 8 Oct 1999, Martijn van Buul wrote:

> The maximum capacity of a cd-Audio is 441000 (samples/s) * 4 (
> bytes/sample) * 74 * 60 = 746.9 MB, while the maximum capacity of a 
> normal CD-ROM is only 650 MB.

I thought about this last night, and also thought about a CRC check.
There's no time to do that on-the-fly, while reading the bits from the
cassette port.  All the loader can do is to report a ?LOAD  ERROR after
completing the transfer and the checksum calculation.

But I still think that this idea is worth trying.  What we need is four

1. a simple adapter from line-level CD audio output to the cassette port
(an RCA plug and a cassette port connector).  The frequency of the signal
should be doubled, i.e. a change in the input must be translated to a
pulse in the "cassette read" signal.

2. a program that stores Commodore tape format in a sample file that can
be processed e.g. by cdrdao.

3. a program that converts files to the new GCR format

4. 6502 software for reading the new GCR format

Step 3 should be trivial after step 2.  Any takers for steps 1 and 2?  I
wouldn't like to learn the details of the Commodore tape format.

BTW, did I mention that the same hardware will work with all 8-bit
Commodores, from the PET to the C128?  (Maybe even the C65, if it has a
cassette port.)


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