Serial port rates

[Don Y]

I just threw together a 1P terminal server to give me
"console" access to one of my UPSs that doesn't have
a NIC.

I figure it would be a great "stocking-stuffer" for *next*
year -- inexpensive ($10 finished price?), small (so I
can mail them to colleagues), simple UI, etc. And,
above all, "convenient" to have on hand!

It's a low, average data rate application (the *port* is
slow even if talking 100BaseTX) so a tiny, cheap MCU/SoC
can handle the workload (the encryption is the most costly
process involved). Most of the code is network stack
so that's a no-brainer.

But, trying to sort out the worst case data rate is
an issue. Of course, 9600 is common. Replaced by 19.2.
But, I also see 115k in some places. Maybe settle for
230K and assume anything needing faster can find another
solution?

[Jasen Betts]

Post by Don Y
I just threw together a 1P terminal server to give me
"console" access to one of my UPSs that doesn't have
a NIC.
I figure it would be a great "stocking-stuffer" for *next*
year -- inexpensive ($10 finished price?), small (so I
can mail them to colleagues), simple UI, etc. And,
above all, "convenient" to have on hand!
It's a low, average data rate application (the *port* is
slow even if talking 100BaseTX) so a tiny, cheap MCU/SoC
can handle the workload (the encryption is the most costly
process involved). Most of the code is network stack
so that's a no-brainer.

can buy that for a few bucks yeah.
https://www.aliexpress.com/item/1005006544010421.html

Post by Don Y
But, trying to sort out the worst case data rate is
an issue. Of course, 9600 is common. Replaced by 19.2.
But, I also see 115k in some places. Maybe settle for
230K and assume anything needing faster can find another
solution?

sometimes oddball rates are useful.

eg: DMX is 250K MIDI is 31K25
also you can do WS2812B 3 bits per byte at 250K 7N1

I came across something that was 1M, but I forget what it was.

[Don Y]

Post by Jasen Betts

Post by Don Y
I just threw together a 1P terminal server to give me
"console" access to one of my UPSs that doesn't have
a NIC.
I figure it would be a great "stocking-stuffer" for *next*
year -- inexpensive ($10 finished price?), small (so I
can mail them to colleagues), simple UI, etc. And,
above all, "convenient" to have on hand!
It's a low, average data rate application (the *port* is
slow even if talking 100BaseTX) so a tiny, cheap MCU/SoC
can handle the workload (the encryption is the most costly
process involved). Most of the code is network stack
so that's a no-brainer.

can buy that for a few bucks yeah.
https://www.aliexpress.com/item/1005006544010421.html

Only makes sense if *it* fits your needs (or, is VERY
well documented, source code, etc.)

Post by Jasen Betts

Post by Don Y
But, trying to sort out the worst case data rate is
an issue. Of course, 9600 is common. Replaced by 19.2.
But, I also see 115k in some places. Maybe settle for
230K and assume anything needing faster can find another
solution?

sometimes oddball rates are useful.
eg: DMX is 250K MIDI is 31K25
also you can do WS2812B 3 bits per byte at 250K 7N1
I came across something that was 1M, but I forget what it was.

This was a common "request" I received when polling the
intended recipients. Though oddball was wanted because
they are deliberately running their diagnostic serial
ports at weird rates and protocols to confound "hackers"
who can easily recognize an RdTd UART's pins on a PCB,
even if unpopulated.

I.e., don't EMIT anything until you *see* something
specific -- so a hacker can't poke at the port and
watch to see how it responds (you've got to know exactly
HOW to "poke" lest it not acknowledge you; get the bit
rate, framing, parity, data, etc. wrong and it "plays
dead").

On the network side, IPv6 & IPsec were "required" along
with similar stealth operation (so they could leave the
adapter in place at a remote site and KNOW that no one
could poke at it in much the same way that the serial
port is obfuscated). Plus a variety of mechanisms to
safeguard its "privileged" role -- you aren't making
a network *appliance*!

[There are a list of other "wishes" -- once you have a
full stack in a tiny box, it's easy to imagine adding
all sorts of far side interfaces (I'm going to throw
them into "network controlled power relays" to allow
powering up/down appliances without having to resort to
unplugging wall warts, servers, etc.). I will let each
of the "recipients" add whatever hardware and slushware
they want to *their* units, having already done all of
the heavy lifting...]