[time-nuts] FE-5680A OSMT connector / RS232

gary lists at lazygranch.com
Mon Dec 10 08:20:18 UTC 2012

The trip point is specd to be between -3 to +3, which is why 5V works, 
especially since the trip point is usually positive. I would set it 
around 1.5V. The transmitters are required to swing +/- 5V.

I'm not sure the 232 "allowed" lower voltage as much as all we had to 
work with were charge pumps, first off a 5V rail and later 3V. Basically 
the voltage was dropped closer to the spec limit to ease the design, 
even if some non-compliant parts wouldn't work on the lower voltages.

On 12/9/2012 11:25 PM, Hal Murray wrote:
> james at peroulas.com said:
>> I'm not able to get it to respond to the 'S' command and when I measure the
>> voltage on the RS232 TX pin (#2 from the left) it's always 0v. Shouldn't it
>> be -12v when idle?
> Newer RS-232 allows 6V rather than 12.
> In practice, it's not all that uncommon for designers to save a chip and just
> send 5V CMOS signals.  That works fine for short distances.
> If you can get a scope on it, sometimes embedded boxes send out a hello
> message at power up.
> I'd also check pin 3 in case you or they got things swapped.

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