2 Feb
2025
2 Feb
'25
6:42 p.m.
On Sun, 2 Feb 2025, Maciej W. Rozycki wrote:
I forgot to mention: MIDI has been another notable example where you want
to wire a UART to another kind of line driver. I also have a computer
where one of USARTs is multiplexed (software-configurable) between an
RS-232 line driver with an external DE-9 connector (with pins multiplexed
between synchronous-mode TxC/RxC clock lines and asynchronous-mode CTS/DSR
inputs respectively) and an AC'97 audio codec (the codec uses the USART's
synchronous mode with internal clocking). This one obviously also uses
regular voltage levels to talk to the AC'97 device.
FWIW,
Maciej
What I meant
is that a lot of modern computer modules come with serial
ports that are not RS232 but rather using standard logic levels (TTL 0
and 5 volts, or perhaps lower voltages such as 0 and 3.3 volts) for
their signaling. Those basically just expose the logic level I/O of the
UART or the embedded serial port.
That makes sense to me since you can then choose what "phy" to attach to
it: RS-232, RS-422, IrDA, etc. It's been done since forever, for example
I think all DEC Alpha machines had their CPU's debug UART wired to a pin
header, but it was up to you to add a line driver if you wanted to make it
a real serial port.