Re: HP 97 problems - a question Message #4 Posted by Tony Duell on 24 May 2004, 2:43 p.m., in response to message #3 by Vieira, Luiz C. (Brazil)
For the 65, 67, 97 and 41, there are 2 tracks in each direction on the card. A magnetic transition on one track is a '0', a transition on the other track is a '1'. It's a simple self-clocking scheme. The same idea, BTW, is used for the tape cassettes on the 9830, with a transition on both tracks being an end-of-byte marker.
For the 71 and 75 I believe there's a timing track and a data track in each direction.
For the 9100, 9810, and I believe 9820, there are 4 tracks in each direction. 3 data tracks and a timing track. This suits the 6-bit keycodes used by the 9100 and 9810 (odd bits, even bits split, BTW!) but is less suitable for the 8 or 16 bit words of 9810 data or 9820 characters.
|