I've got Arduino Pro Mini and I want to connect its RX/TX pins to external USB MIDI microcontroller, Altmustech AU-123 to be precise. Now, since that chip accepts 0-5V on MIDI In/Out pins, I am assuming it should be as straightforward as simply plugging those pins to Arduinos RX/TX. If I'm right, that still leaves me GRN pin on Pro Mini. That pin is for auto-reset, right? I connect it to DTR line to my CP2102 converter, but in case of connecting it to that external chip, should I leave it unplugged? Or connect it to ground? Something else?
GRN pin? What does that mean?
raschemmel:
GRN pin? What does that mean?
The RTS pin, labeled "GRN" as it corresponds to the green wire to the connector on the "standard" FTDI cable.
Ok. Thanks Paul. I wasn't expecting that.
Leave it connnected unless you plan to implement hardware flow control, in which case you'll need a bunch of other connections as well.
CrossRoads:
Leave it connected unless you plan to implement hardware flow control, in which case you'll need a bunch of other connections as well.
I think the point was that he wants to connect the (hardware) serial interface to the MIDI board, not the CP2102 USB interface, and was wondering whether this pin needed to be connected to anything.
The answer is no - no need to to connect it to anything, just let it hang loose. 
Yeah, that was supposed to be "unconnected". Fingers not quite in sync with the brain.
Paul__B:
I think the point was that he wants to connect the (hardware) serial interface to the MIDI board, not the CP2102 USB interface, and was wondering whether this pin needed to be connected to anything.The answer is no - no need to to connect it to anything, just let it hang loose.
Yes, that's what I wanted! Thanks. Still wondering about RX/TX pins. I guess they just connect directly, after all it's microcontroller-to-microcontroller communication.
kustom:
Yes, that's what I wanted! Thanks. Still wondering about RX/TX pins. I guess they just connect directly, after all it's microcontroller-to-microcontroller communication.
A MIDI device needs one cable in each direction (in / out).
It also uses optocouplers on the inputs, which is what you need to drive with the Arduino's serial output. ie. It's not just TTL logic, it's more like lighting up a LED with the output pin.
You need to read the MIDI specs before connecting anything.
fungus:
You need to read the MIDI specs before connecting anything.
Actually, research on the AU-123 chip reveals that it is in fact, a USB to TTL converter chip functionally similar to the CP2102, intended to provide MIDI connectivity if you provide the MIDI buffers and optocouplers. MIDI being a fairly standard serial protocol at a specified baudrate.
So - if the polarity of the Tx and Rx is appropriate - I didn't look that far - you can essentially use it in place of the CP2102.
Paul__B:
fungus:
You need to read the MIDI specs before connecting anything.Actually, research on the AU-123 chip reveals that it is in fact, a USB to TTL converter chip functionally similar to the CP2102, intended to provide MIDI connectivity if you provide the MIDI buffers and optocouplers. MIDI being a fairly standard serial protocol at a specified baudrate.
So - if the polarity of the Tx and Rx is appropriate - I didn't look that far - you can essentially use it in place of the CP2102.
Awesome, that's what I wanted to know. Thanks.