[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 

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.

These are my opinions.  I hate spam.

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