Re: JiffyDOS transfer protocol: Any documentation available?

From: Jim Brain (
Date: 2004-10-21 05:44:56

Spiro Trikaliotis wrote:

>Anyway, as JD seems to be quite synchronous - which is not good for a
>multitasking, non-RT OS - I doubt it will be possible to have good
>support for it. I hoped JD to be truly asynchronous.
I think your terms are backwards (JiffyDOS is very timing dependent, 
like RS232, which is called asynchronous operation, but I know what you 
are saying.

It might be possible, as JDos syncs with data at the start of each byte, 
as I recall, but then the byte comes in 4 half nybble (twobits?) chunks 
of 13-14uS intervals.

on the trace I have:

time 0 data goes high to signal new byte. (not sure which side does 
this.   I think receiving side)
time 7 first 2 bits
time 20 next 2
time 34 next 2
time 47 last 2
time 54 release data line to high
time 62 other side acks by bringing low.

If you can kills IRQs for 60uS or so, you might be able to do it, as 
long as the code you have can hit each of the twobit times within 7uS 
(sample at midpoints: 14,28,42,49 uS +- 3 uS or so)

Jim Brain, Brain Innovations                      
Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times!

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