[Elecraft] K2 - KIO2 stop bit oddity

[David Woolley (E.L)]

Brian Lloyd wrote:
> 
> The receiver's stop-bit setting needs to be greater than or equal to the 
> stop bit setting of the transmitter. It is OK for the transmitter to 

You meant less than, not greater than, although, as you noted later, 
receivers generally don't have a stop bits setting.

> send two stop bits and for the receiver to be set for one stop bit. It 
> won't hurt a thing. Most UARTs use the stop bit setting to affect only 
> the transmitter (RS-232 sending part of the device). The receiver will 

Delete RS232.  (In fact, historically, current loop was used for the 
physical interface.)

> handle anything that is at least one bit-time long for a stop bit. 

Modern UARTs accept stop bits that are just over half a signalling unit 
in length (they sample in the nominal middle, but there is a limited 
sampling clock resolution.  They need to accept ones that are strictly 
shorter than the transmitted ones, because, as we are talking about 
asynchronous signalling, they need to be able to cope with recovering 
from false start bits and cope with clock rate differences (more common 
on mechanical devices, but some electronic devices rely on these to 
allow working with convenient crystals.

(When sending asynchronous data over 1200 bps synchronous modems, 
sometimes no stop bits could  be sent over the wire, if the source clock 
was fast, as, being synchronous, there was no option to shorten the stop 
bit.  Stop bits were re-inserted before creating the baseband output; I 
believe they ran the output clock fast to ensure that this worked.)


> Longer stop bits just reduce the maximum rate (characters per second) 
> that you can send data.

And give better recovery from false start bits - not a problem you 
should have on a short piece of wire.

Incidentally, 4800 baud is normally sent with one stop bit.  As noted 
elsewhere, it is only really for mechanical devices that one needed 
longer ones, so it tends to be 110 and below (maybe 300) that uses 2, or 
for, 5 unit, Baudot, 1.5.
> 

-- 
David Woolley
"The Elecraft list is a forum for the discussion of topics related to 
Elecraft products and more general topics related ham radio"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>