#THIS IS AN ARCHIVED USENET MESSAGE FROM 1997 Subject: Re: Kansas City cassette recording format From: ab528@FreeNet.Carleton.CA (Heinz W. Wiggeshoff) Date: 1997/12/09 Message-ID: <66k4ge$2ae@freenet-news.carleton.ca> References: X-Given-Sender: ab528@freenet5.carleton.ca (Heinz W. Wiggeshoff) Reply-To: ab528@FreeNet.Carleton.CA (Heinz W. Wiggeshoff) Organization: The National Capital FreeNet Newsgroups: alt.folklore.computers Stephen Crane (jsc@outoften.doc.ic.ac.uk) writes: > Anyone out there got any technical information about this? I have > some cassettes of varying age and quality whose information I'd like > to retrieve, preferably using my PC's audio card. Ideally, someone > will have written a program for Linux which does this but, given the > info, I'll have a bash at it over Xmas. From Microprocessor Interfacing Techniques by Austin Lesea and Rodnay Zaks (whatever happened to him?) c/r 1978 SYBEX Inc. ISBN 0-89588-003-2 p. 128 KANSAS CITY STANDARD In order to use these inexpensive recorders in the hobby market, a standard was proposed and adopted by hobbyists. Using frequency shift keying techniques, and frequency double frequency [sic] modem techniques, this standard is easy to use. The drawback is the data rate of 30 characters per second. The system takes standard serial RS-232C data ... and converts each bit to either 8 cycles of 2400 hertz (a "1") or 4 cycles of 1200 hertz (a "0"). To generate this, only a few flip-flips [sic] are required along with a quad NAND gate. Shown in Fig. 4-55 is the modulator. [Image sent on request] [Circuit function, ditto] The demodulator must detect whether 1200 hertz or 2400 hertz tones are present. There are many ways of doing this; however a common one is to detect zero crossings of the input signal. This will generate either 2400 or 4800 pulses per second. [Circuit details sent on request] The circuit for the demodulator appears in Fig. 4-56. The de- modulator timing appears in Fig. 4-57. Note how one gets back what one started with, along with the necessary clock information. If the tape speed varies, the data may still be recovered as the clock information will insure the UART receives the proper timing signal. No special software is needed as this interface makes the cassette look like a paper-tape, punch-reader combination to the computer. [Images sent on request] (This format is found between the KIM cassette interface, and the One Chip Digital Cassette controller using the NEC UPD371D.) (Surprisingly, the documentation for my Heathkit ETA-3400 only mentions the frequencies, not the details of the encoding.)