break on pdp11 serial ports

[Sytse van Slooten]

Hello all,

I've been playing around with some ideas for designing some hardware to 
connect peripherals to an fpga for my vhdl pdp-11. One of the things that 
should definitely be on there, next to sd cards and leds... are some serial 
ports for console terminals etc. I've spent some time to create a prototype 
usb to serial thing that handles more than one port. Works kind of neat.

While doing that, I stumbled on the concept of break. Up to now in all of the 
pdp2011 history I have ignored it, the serial port that sits at the pdp-11 
side of things is about the most minimum that does the job. And that is good 
enough for a lot of things, actually - I didn't really miss a break signal so 
far.

Anyway, 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.

That's where the questions start. How did a DL-11 like interface signal the 
reception of a break? And how did the operating systems and software deal with 
it? Was it actually used at all? 

I think to remember several occasions of impatiently banging the break key 
back in the day, but it is a bit fuzzy why (and if it had any result).

anyway, I'm trying to judge whether it makes any sense to put effort into 
making the break thing work on my serial converter thing... any kind of input 
is greatly appreciated!

cheers
Sytse