Pololu 23201a Serial Adapter Partial Kit

A probably typical question regarding RS232 adapters, but I didn’t find a discussion here

There are RX and TX pins on both sides of the adapter, the incoming side and the outgoing side.
I call the the UART side (10 pin side) the In-side and the Sub-D9-side I call the Out-side

Is it correct, that within this adapter
RX on the In-side is connected to the TX on the Out-side (D9) and
TX on the In-side is connected to the RX on the Out-side (D9) ?

And does
TX on the Out-side (D9) means that the serial adapter is sending on the Out-side (D9) while
RX on the Out-side (D9) means it is listening on Out-side (D9)?


As described in the product page description, the TX line and RX lines on the board are labeled from the computer’s perspective, so the TX pin has data transmitted by the computer that should be connected to your project’s receive input.

For more details, I suggest reviewing the datasheet for the MAX3238 from Texas Instruments. (This adapter is effectively a carrier board that chip.)

- Patrick

Hi @PatrickM

Thank You for answering. I had checked these links before, but wasn’t clear with that.

There are two sides of the serial adapter, the 9pin D9 side and the 12 pin UART side.

So I just want to make shure, if my expectation is correct, to contact

  • The Pololu’s D9 TX to the Computer’s serial RX port and
  • the Pololu’s UART side RX to the micro controller’s serial TX port ?

I do not think your first bullet is a good way to think about those connections. The only thing that should go between the DB9 connector on your computer and the DB9 connector on the adapter is a DB9 cable which will make all of the correct connections. If you are planning to use jumper wires instead, or somehow make your own cable, then I suggest looking at a pinout for DB9 connectors, like this one I found from a quick internet search, and making sure the right pins get connected to each other based on the physical pin numbers.

For the other side, you are correct. The adapter’s RX pin should be connected to your microcontroller’s TX pin, and the adapter’s TX pin should be connected to your microcontroller’s RX pin.

- Patrick