On Sep 13 14:33 96, Ian Smith of 3:626/660 wrote:

LE>> particularly impressive. Actually there was an interesting
LE>> discussion here (or zone3_tech?) about the fact that RS232
LE>> is NRZ, so therefore doesn't have a "baud rate" per se
LE>> possibly.

IS> RS232 is Non Return to Zero?  I don't believe so.  As far as I know, it's 
IS> straight 0 (start bit), data bits as they come, then 1 (stop bit), per 
IS> byte.

IS> NRZ (or NRZI) is usually used on self-clocking data streams, is it not?  
IS> RS232 as we use it is referenced to fixed (local) Rx/Tx clocks, clocked at 
IS> mid-bit.

The data stream doesn't change from bit to bit, if the data value doesn't.
There is no embedded clock transition.   

NRZI is similar, with the data being toggled for a 1 bit, and left static
for zero.  For that one, a constant stream of zeros gives constant polarity
of whichever was showing when the constant stream started.  Still no
embedded clocks.  The spectrum had some advantages on lines that could go
quiescent in mark state, which is where it came from.

Embedded clocks don't show up until you get to bit stuffing, or go to FM or
MFM encoding.

NRZ is (N)on (R)eturn to (Z)ero encoding.  The reason for the start and
stop bits is that when the format was designed, 8 data bits was just about
the limit for accuracy of the local sampling clock.  (It was
mechanical..:-)

Regards,
Dave Hatch.

--- Msgedsq 3.20