[GreenKeys] 7.00 vs 7.42 unit code

[Harold Hallikainen]

> Doing some machine shuffling this week made me think about this - please
> steer me back on course if my thinking is off.....
> Truth-
> 7.42 unit code has a start bit and 5 data bits of equal length (1.00 unit
> each) and a stop bit 1.42 units long.
> 7.00 unit code has a 1.00 unit stop bit.
> 45.45 baud code can be either - each 1.00 unit data bit is 22ms.
> So 7.42 unit at 45.45 baud is 60 wpm
> and 7.00 unit code at 45.45 baud is 65 wpm
> There's a chart at http://www.navy-radio.com/tty/speed-feed.gif
>
> Consequences-
> These two do require different gear sets - you can't just put 60wpm gears
> (368 opm) into a 7.00 unit machine (390 opm) - that would make the baud
> rate wrong and your selector and keyboard transmitter timing would be off.
> A 7.00 printer can copy a 7.42 keyboard or 7.42 TD no problem.
> A 7.42 printer can copy a 7.00 keyboard if you don't type at max rate
> A 7.42 printer probably cannot copy a 7.00 TD
>
> What about sending RTTY with a 7.00 keyboard or TD? - will the computer
> software RTTY folks copy it OK? I assume so, but don't know for sure.
>
> Comments welcome.....
>
> best regards,
> Nick England K4NYW
> www.navy-radio.com

>From my RTTY stuff 50 years ago, while in high school, I remember all the
bits as 22 ms except for the stop bit, which was 31 ms. A lot of UARTS let
you set the stop bit to 1, 1.5, or 2 bit lengths. A longer stop bit is, of
course, perfectly fine when it hits the receiver since it looks like a
short idle line period between characters. A shorter stop bit than
expected, though, COULD cause the leading edge of the start bit to be
missed. I don't really know how all the cams in a printer are set up. It
SEEMS like they would sample the stop bit 22 ms after they sampled the
last data bit and, if mark, stop the shaft from rotating. I see no reason
to sample later, even though the stop bit MAY be longer. In a software
UART I designed in a product that measures the chromaticity and luminance
of the projected image on a movie screen, I send "pulses" of light to the
screen at 0.5 bits per second. The character is decoded and a measurement
script run based on the character that was decoded. In that system, I use
an 8 bit ASCII character with the most significant bit 0 (space), so there
is always a 0 to 1 transition at the beginning of the stop bit. I start my
script on that edge.

Back to electromechanical, again, I don't know the actual design, but on
the receive side, I see no reason to not just sample the stop bit (and
stop shaft rotation) 22 ms after the sampling of the last data bit, which
would be 11 ms into the 31 ms stop bit. To know for sure, it would be
interesting to get some slow motion video. How long is the shaft stopped
for?

Harold




-- 
FCC Rules Updated Daily at http://www.hallikainen.com
Not sent from an iPhone.