> On Jan 31, 2025, at 10:37 PM, Maciej W. Rozycki <ma...@orcam.me.uk> wrote:
>
>> ...
>
> The serial port hardware I refer to uses a UART wired to a Zywyn ZT3243F
> line driver, which according to the manufacturer's datasheet signals at
> ±5V minimum transmitter voltage levels and accepts up to ±25V receiver
> voltage levels and: "Meets or Exceeds the EIA/TIA-232F and CCITT V.28/V.24
> Specifications for VCC at +3.3V ±10% and +5V ±10% Operations." While the
> transmitter voltage levels are not the highest recognised by the standard
> I do believe this line driver does comply with RS-232.
>
> As I say the datasheet explicitly says: "Guaranteed data rate 1000kbps,"
> and according to my findings quoted above it is indeed the case (and well
> beyond). [Yes, I got it wrong by writing 1MHz rather than 1Mbps, a mental
> slip I suppose.]
>
> NB I've also used the TI TRS3122E line driver, suitable for operation
> with 1.8V signalling per my requirement, and it is also documented to
> handle "data rates up to 1000kbps, while maintaining RS-232-compatible
> output levels." I haven't got a chance to go beyond 230400bps with this
> device though, but these two samples do suggest that supported operation
> at 1Mbps isn't that uncommon for currently available RS-232 line drivers.
>
> I've looked up the MAX3222 datasheet and it does say 250kbps max though;
> I guess it's older technology then?
>
> Does this answer your question?
Sure does.
I don't know if the MAX3222 is older, or just different. The RS232 standard
doesn't apply to those high rates. And I vaguely remember seeing words that
imply the line drivers should have controlled rise/fall times. So I think the
MAX3222 limits come from implementing those rate limited edges, not from the
age of the design.
paul
