Serial LCD on imp April board Requires "inverted UART" to tx/rcv signals, can it be done in software

Serial LCD on imp April board Requires “inverted UART” to tx/rcv signals, can it be done in software.
i have a 16 X 2 line LCD, , model BP216, can i use it, or would it be simpler to invert the signal with a hardware inverter.I have it working ok on Arduino, using “software Serial”, where you can code it to invert, SoftwareSerial mySerial(10, 11,true); // RX, TX, easy.

There’s no way to do inverted UART on the imp (it’s not supported by the STM32’s UART hardware).

However, I’d be kinda surprised if it actually needed inverted. TTL UARTs are inverted compared to standard RS232 signaling (ie they idle high, at 3.3/5v, and active is low, at 0v where as RS232 idles at -5 to -12v ish and active is +5 to +12v.

I’ll look at the datasheet when I have usable internet. On a plane and the internet is sketchy to say the least.

Ah. Looked at the datasheet - essentially it’s a “poor man’s RS232” - ie they have clamped the voltages but not used a real serial buffer, so yeah, you do need inverted TTL.

You can do this with a single transistor and a pull-up if you want - simpler than an inverter. Let me know if you’d like a sketch.

I think this describes the same issue:

Looks like a standard 2N2222 transistor.

You are only sending from imp to display (one way)?
In their diagram, the TX is your imp and the RX is the display.

Yep, that’s the diagram I was going to draw :slight_smile: