At 08:32 PM 01/02/1997 +0200, you wrote:
>Hi,
>
>Not on toPIC, sorry.
>
>Here is a link that I found on the net after finding 3 incorrect
>descriptions that is short but correct.
>
>   http://libweb.macarthur.uws.edu.au/comp1.1/cpw11p1.htm

Hilarious! When you find something that matches your definition then "it's
short but correct", and when it doesn't then it's "incorrect".

>
>BPS is for the digital guys and just leave baud to the analog modem guys.

>
>BAUD is equal to BPS for unmodulated data.  When you modulate the
>BPS does not change but you have a choice of encoding multiple
>(yeah or fractional) bits with one change in the signal.

[snipped ... well ... stuff]

>
>What this means is that the bps signal is what you get when connecting
>most digital equipment together with garden variety serial connections
>and the baud only comes into play if you are about to modulate the
>signal.

Who cares really?
>
>This has very little directly to do with PICs or microcontrollers
>but serial communications do get used often and it is safer in
>almost all cases to just use Bits Per Second unless you are into
>modem design.

I agree!

Baud/bps. Until a particular group of 'experts' evolves in this industry the
definitions of what happens or what things are are fairly logical or are
named after a scientist or innovator.

For instance in the communications industry, bytes or characters are _not_
transmitted.  Instead they use octets. (Internetworking with TCP/IP Volume 1
- Principals, Protocols and Architecture - by Douglas E. Comer  ISBN #
0-13-216987-8). Also, Comer states that:

"baud - Literally, the number of times per second that the signal can change
on a transmission line. Commonly, the tranmission line uses only two signal
states (eg. two voltages), making the baud rate equal to the number of bits
per second that can be transfered.  The underlying transmission technique
may use some of the bandwidth, so it may not be the case that users
experience data transfer at the lines specified bit rate.  For example,
because asychronous lines require 10 bit times to send an 8-bit character, a
9600 baud asynchronous transmission line can only send 960 characters per
second."


Here he gives a definition that doesn't even use the word modulate and the
actual number of data bps is 7680.  Program your PIC to bit bang a uart at
7680bps and you won't properly receive the data. Program the PIC to bit bang
at 9600 baud,  strip away the transport information and you get 960
characters per second - correctly.

>Sorry to ramble but I was getting a bit queasy reading the
>urban legends being promulgated as fact.

Quite right.  In the future you may write that we're all so silly to talk
about characters and bytes when they are really _octets_ and that bytes and
characters are urban legends.


>> >I refer anyone wanting more info to The Modem Communication Book (don't
>> >have exact title or author cause that book is at work) for protocol info
>> >and National Semiconductors Communications Databook - good info on EIA
>> >and RS standards.
>
>Good advice, the net seems to be pretty weak on this topic with
>60% of the first 5 sites I checked getting it wrong.
>

Right on.  After all I found a source that states we send octets, not
characters so all the other sources that say we send bytes or characters are
also wrong.  8-)

In either case to get back on toPIC.  If asked to interface to a modem or
other device that is sending data to me at 38K baud I'll still ask if one or
two stops bits are being used, then if parity is included in the 8 bit byte
(or octet) or if it takes an extra bit position and determine if my
application can handle the data load.  Past that for a PIC, who cares if
it's fiber optic light beam on/off at 38K baud or modulated something or
other.  I still get a large number of bytes in per second that my
application has to handle and I may have to strip a certain amount of
transport information to get at my data.


IMHO

John


Pioneers are the ones, face down in the mud,
with arrows in their backs.
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