[EMAIL PROTECTED] wrote:
> >
> > If I am not mistaken, the Parity, Overrun and Framing Error bits are not
> > representing the last byte, but any byte since last time the LSR was read. I.e
> > upon reading LSR is cleared.
>
> My doc says parity/framing error at receiving the last byte. I have not
> the equipment to check this. But the LSR have to be read frequently to
> check if there's a byte, so it should be the same, hm, at least with a
> non-FIFO UART. Ok, I will change the HOWTO.
Correct that you will be reading that register all the time in polling and at every
interupt if that is the way, and by that, the parity/framing will indicate the last
byte. It is mostly an academic question, since if it occurs, a whole packet needs to
be resent (unless data correction is able to handle it).
The FIFO case is more accurate, since it may burst in a couple of bytes before the
status can be read, and you definately needs the "worst-case".
> > And as Lawson says. "Spacing condition" is called BREAK, sending BREAK or
> > breaking
> > condition. A permanent LOW level (-12V) on the RS232 side.
> My doc speaks of 'spacing condition', as opposite of 'marking condition'.
> It's 2:1 for 'breaking condition' :-)
Mark and Space is the terminology for +12V and -12V respectively, typically at bit
intervals. For instance, you may use Space Parity which will be a logical 1 in the
parity bit. (Mark Parity is not very common, since it is eqvivalent to no parity
+ 2 stop bits.)
BREAK on the other hand (and that was the original intension of the BREAK key on the
IBM PC keyboard) is a special purpose signal, normally to interrupt an ongoing
transmission from the other side. BREAK is, if I remember correctly, a Space
(-12V) at least 2 full frames, which at 150 bps (standard speed when this was
invented) became ~100ms (could be the spec?).
I have not heard of any recent use of the BREAK condition.
So, you docs might actually be right, when I think about it. What you need to check,
is whether the UART provide the timing, or if the controller has to do the timing
for that signal. If the controller has to do the timing, then it is correct to talk
about a Space...
Niclas
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