BBB Uart Signal Question

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Mike Brandon

Feb 25, 2019, 12:53:19 PM2/25/19
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TL;DR: What kind of signal is transmitted straight out of UART TX? 

I am beating my head against a wall with a circuit I have been designing related to UART. I know my app works as I can use a USB-to-Serial adapter connected to beaglebone's USB0 and my app performs as expected. When I attempt to use UART4, via a MAX3232 chip, the app does not communicate as expected. Prior to placing the MAX3232 chip in my circuit, I remember having unsuccessful attempts with my app as well, leading me to believe that I needed to convert the signal coming out of the UART with the 3232 chip.

The device I am communicating with also has a 3232 chip onboard that my signal is going through. I a thinking I am misunderstanding the signal being produced by the UART4. I know I have at some point confused what results I was obtaining when I had the circuit breadboarded and was testing things out. So I think I am just needing to start fresh and do some better documenting of my tests going forward.

However, at this current point in time, I do know my MAX3232 circuit works as I have tested by looping the RX/TX lines on the other side and I can send/receive in minicom on the BBB. I also communicated with another PC via the circuit successfully. In that setup, the BBB was sending through the MAX3232 which the RX/TX output was connected to a USB-to-serial adapter that was connected via USB to a windows PC.

I have also a better documented thread of the issue here, for reference:

At this point, looking at my circuit and the device I am attempting to communicate with, I believe I am sending a TTL signal to the device connection which is expecting a RS232 signal. 

Mainly I am just trying to understand what kind of signal is transmitting out of the UART TX, is it TTL or RS232? I did look at the BBB system ref. manual but did not see data related to this.


Robert Nelson

Feb 25, 2019, 1:05:49 PM2/25/19
to Beagle Board, Mike Brandon
On the bbb it's 3.3v TTL


Robert Nelson


Feb 25, 2019, 1:09:07 PM2/25/19
3.3v ttl

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