On Wed, Jul 30, 2025 at 08:46:49PM -0400, Greg Wooledge wrote:
> On Thu, Jul 31, 2025 at 01:38:15 +0100, mick.crane wrote:
> > serial console/ parallel is likely me not understanding terminology.
> > These Raspberry Pis, Arduinos with the connection with all the pins, what
> > protocol is that expecting?
>
> A serial cable usually has a 9-pin (DB-9) connector on each end.
> A parallel cable usually has a 25-pin (DB-25) connector on one end,
> and either another DB-25 connector or a mini-Centronix connector on the
> other end.
They also had 25 pin, but they were the other way around :-)
It's confusing, I know. This thing has had a very long life, therefore
it presents itself under many incarnations.
Serial console is actually a misnomer. Serial interface in a way also,
but it usually refers to RS-232, originally a way to connect a terminal
or modem ("DCE") to a computer ("DTE"), see [1], for the connector and
hardware part, [2].
The "serial" thing refers to the fact that data are transmitted one bit
after the other, so you don't need that many wires (it's bidirectional,
therefore you need strictly speaking two plus "electrical stuff" like
ground. But there are many support functions like flow control ("HOLD
ON, I CAN'T GO THAT FAST"), device readiness indicators, etc. etc
(for the modem, there's a "ring indicator", for "the phone is ringing",
for example).
The "serial" term is confusing in itself. USB is serial (or, for
USB-C a bundle of serials), PCI express is also serial. Most high
speed lines these days are serial [3], mainly because it's easier
and cheaper to pick apart clocking protocol at the ends than to
fix timing skew and electromagnetic noise across a bundle of lines
which are supposed to walk in sync.
Cheers
[1] https://en.wikipedia.org/wiki/RS-232
[2] https://en.wikipedia.org/wiki/Serial_port
[3] https://en.wikipedia.org/wiki/PCI_express#Serial_bus
--
t
Attachment:
signature.asc
Description: PGP signature