> From: Sytse van Slooten > digging through the documentation of KL-11 and DL-11 I did find > references to generating a break (bit 0 in the XCSR). But not on how it > would be received. ... How did a DL-11 like interface signal the > reception of a break?
As JohnW says, framing error. FWIW, the UART chips used back then actually produce a 'framing error' output, which is sent straight into that bit in the RCSR. > And how did the operating systems and software deal with it? Was it > actually used at all? Different systems used it for different things. Unix V6 used 'break' on dial-up lines as the signal to switch speeds when you first connected up - it would try 110, then 150, then 300. (Later this got extended, I expect - too lazy to check.) I see the hacked PWB1 Unix at MIT used it to send an interrupt: if (c & FRERR) { signal(tp->t_pgrp, SIGINT); return; } That's as far as my knowledge extends, others may know of more uses. Noel