[time-nuts] SRS PRS10 repair
Hal Murray
hmurray at megapathdsl.net
Tue Aug 25 20:36:26 EDT 2015
> Hang on a minute, polarity does not switch all of a sudden.
The standard RS-232 interface chips include an inverter. The normal output
from serial pins on microprocessors or PCI/USB serial chips expects that
inversion.
For short runs where you are designing both ends, it's common to skip the
RS-232 drivers.
So if you are trying to talk to something like a GPSDO board without the
typical 9 pin serial connector, there is a reasonable chance you may need to
add an inverter. (or maybe a real RS-232 interface chip)
--------
It's also possible to cheat on the RS-232 interface ship. A TTL/CMOS driver
will work with most RS-232 receivers and a resistor with maybe a pair of
diodes will protect a CMOS receiver from RS-232 levels. If you are doing
that, you need an inverter in there someplace. With a microprocessor, the
inverter is often available (for free) in the pad driver.
--
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