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One thousand baud cassette interface on Model One

Floppies_only

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Gang,

I was looking through the December 1978 issue of "Kilobaud" and it gave a source code listing to speed up the cassette interace of the TRS-80 model 1 to 1000 baud. It said that the level one machine operated at 250 baud, and level 2 operated at 500 baud. The author said that by loading this code (modified from that in ROM) and executing it he was able to load a 14k program in two minutes, down from 7 1/2. The one thing he did not say was how many errors there were in the program when it was loaded at that speed, making it sound as if there weren't any. Perhaps Radio Shack was trying to sell more expansion interfaces and disk drives.

My local university has these magazines available for the public to view, and copy machines to use, too. Perhaps a trip to your local university will yield some valuable nugget of information.

Sean
 

Druid6900

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I'm familiar with the TSR program you're talking about and it worked pretty well, if you had the "G" revision board or an earlier board with the XRX-3 cassette load mod.
 

mbbrutman

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I don't think that Radio Shack was trying to be dishonest. Cassette players were not high fidelity devices, so running them slower improved your chances of getting a good read or write. It also compensated for tape speed differences, wow and flutter, etc.

If you are interested in seeing what the waveforms actually look like, take a look here:

http://www.brutman.com/Cassette_Waveforms/Cassette_Waveforms.html

Those are from an IBM PC, but the basic concepts are the same for any cassette based system. (The PC uses a variable baud rate, which is an oddball.)
 

Floppies_only

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I don't think that Radio Shack was trying to be dishonest. Cassette players were not high fidelity devices, so running them slower improved your chances of getting a good read or write. It also compensated for tape speed differences, wow and flutter, etc.

If you are interested in seeing what the waveforms actually look like, take a look here:

http://www.brutman.com/Cassette_Waveforms/Cassette_Waveforms.html

Those are from an IBM PC, but the basic concepts are the same for any cassette based system. (The PC uses a variable baud rate, which is an oddball.)

"Anybody who was forced to use a cassette on any machine would immediately buy a diskette drive, no matter what the cost."

Ha! Not my Dad.

There's another factor, too. The faster you do frequency shift keying (what that is called), the more bandwidth it takes up. But the bandwidth (frequency response) of the tape recorder is fixed, so if you speed up too fast, it is going to stop working.

I remember back in the day when cassette recorders in boom boxes often had a "copy at two times speed" feature. I told a co-worker who was musician that it would cut off the high frequency response, but he explained that no, I was wrong. Sadly, I can't remember what his explanation was, but I do remember that it made sense at the time.

Sean
 
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