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 > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.