[time-nuts] SRS PRS10 repair

[ziggy9+time-nuts at pumpkinbrook.com]

This was exactly the case on my Rb. It was suggested by the OEM that one
could directly connect the 0/5V serial connection to a PC "RS232" serial
port (but with the warning that reversing the TX/RX connection could
destroy it). So the polarity was inverse from what you'd normally expect
on a 0/5V interface, but the same as RS232. As a result of the caution
from the OEM I decided it was much safer to use a real TTL level
interface and the reprogramming of the FTDI chip solved the polarity
issue. Easy and safe. Your NPN inverters/level shifters will work just as
well of course. Congratulations on getting it talking.

On 08/26/2015 12:28 AM, Brian M wrote:
> Hi -
>
> So I took the time tonight to poke at things with the scope. Hopefully it
> will be of interest.
>
> First off, I probed the MCU (MC68HC11) TX line directly. And, it looks like
> I misstated in my last mail. The MCU itself is 5V TX idle TTL Serial. On
> the unit's output, it is inverted and 0V idle. Not sure why that's the
> case...
>
> That said, I have lashed up some simple NPN inverters which are also
> level-shifting to a BBB UART. And with that I've got serial comms
> established. I get the power-on message and response from "ID ?" is "
> PRS10_3.24_SN_[....]"
>
> Thanks again to all for their input. Always more to learn =)
>
> - Brian
>