Richard <legalize at xmission.com> said: Short answer: Neither. Long answer: 2741's came in two flavors, "correspondance" and "BCD" (someting close to PTTC/8). The serial code transmitted is 6 bits and parity (total of 7 bits) with start and stop bits. In PC parlance: 6E1. The transmission speed is 134.5 bps. Most baud rate generators actually have this speed. The tricky part of this is that the 2741 communicates in HALF duplex. It has character codes that turn the line around. On the terminal proper the <return> key and the <attn> key. If you actually have a 2741, it might have manuals in its back which describe some of this stuff (cryptically as I remember it). If you want to release the typing mechanism, you can QUICKLY cycle the power and it will release. The difference between the codes is only the position on the ball and the encoding of the keyboard. If you feel up to it, you can use the other type of ball on the foreign machine. You need to send it the right codes. The keyboard can't be changed, so if you have the wrong code, it types "wrong". Why two codes? History. Correspondance code was what they used when they coded the original typeball on the selectrics (before they were used for computer I/O). They made the ball that way to minimize thavel for frequently used codes and to not have pairs of large letters (like M and W) next to each other. The BCD codes were used when they adapted the units to computer use. IBM changed the keyboard coding on the BCD units (there is some documentation on bitsavers) to correspond (bad word in this context) to what they changed the typeball to. Simple facts: The typeball has 88 positions. Two shifts, 44 in each shift. There are 4 tilt positions and 11 rotate positions (neutral and 5 each way left and right). At least that is the way on Selectric 1's and 2's. Selectric 3's have 96 positions. Inside the typing unit, it takes 6 bits to make something happen: Tilt-1, Tilt-2, Rotate-1, Rotate-2, Rotate-2A, and Rotate-5(minus). The 2741 has codes (that don't type) much like an old 5-level teletype to do shifts (upper case/lower case) and space. backspace, index (we call it line feed) and return (CR and LF combined). Just so you know: There is a symbol B134 in /usr/include/bits/termios.h on the Linux box I'm typing this on. The speed is actually 134.5 bps. See the man pages Another wierd fact: Normal baud rate generators (and uarts) use a 16x clock. For 134.5 bps this is 2152 cps. This is very close to a modem tone used in 103 type modem (2025Hz and 2225Hz). It can really screw up accoustic couplers (I found out the "hard way"!). Wierd fact: When IBM contracted with Qume for the units in wheelwriters, they used correspondance code on their printwheels. Qume had an awful time since some of the tines on the wheel had adjacent "high density" codes. Wierdness compounded. We now return you to the regularly scheduled mailing list for even more trivia... -- Tom Watson tsw at johana.com __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com