user25651: I can't access my Arduino Micro's USB programming port when it's in my project. I want to reroute the RX and TX pins outside to a serial-to-usb adapter.
I have this on hand from a while ago. I found the RX and TX pins in the serial connector and I connected them to the RX and TX pins of the Arduino as well as GND but when I try and program the device nothing happens. I usually get an open port error or something like that but the programming LED on the adapter doesn't light up. Conversely if I try using the Basic Stamp software I at least get a programming LED to light up on the adapter.
Do I need an FTDI breakout instead? Or am I wiring something wrong?

user31361: RS-232 logic uses a negative voltage typically from -3 to -25V to represent a logical high and a positive +3 to +25V to represent a low. On the flip side TTL used on the AtMega uses +5V or +3.3V as a high (or VCC) and 0V as a low. Read more
Other than that the signals are the same logically so all that is needed is to invert the RS232 from -/+ ~12V to 0-5V using a simple converter.
Possibly the easiest approach is to use another Arduino Uno as a programmer, which needs 3 pins, TX, RX, and RESET. This tutorial seems to have some success. Check out "programming an Arduino with another".

25651: <p>I can't access my Arduino Micro's USB programming port when it's in my project. I want to reroute the RX and TX pins outside to a serial-to-usb adapter.</p>

<p>I have <a href="https://www.parallax.com/product/28030" rel="nofollow noreferrer">this</a> on hand from a while ago. I found the RX and TX pins in the serial connector and I connected them to the RX and TX pins of the Arduino as well as GND but when I try and program the device nothing happens. I usually get an open port error or something like that but the programming LED on the adapter doesn't light up. Conversely if I try using the Basic Stamp software I at least get a programming LED to light up on the adapter.</p>

<p>Do I need an FTDI breakout instead? Or am I wiring something wrong?</p>
 31361: <p>RS-232 logic uses a negative voltage typically from -3 to -25V to represent a logical high and a positive +3 to +25V to represent a low. On the flip side TTL used on the AtMega uses +5V or +3.3V as a high (or VCC) and 0V as a low. <a href="https://www.sparkfun.com/tutorials/215" rel="nofollow noreferrer">Read more</a></p>

<p>Other than that the signals are the same logically so all that is needed is to invert the RS232 from -/+ ~12V to 0-5V using a <a href="https://www.sparkfun.com/products/449" rel="nofollow noreferrer">simple converter.</a></p>

<p>Possibly the easiest approach is to use another Arduino Uno as a programmer, which needs 3 pins, TX, RX, and RESET. This tutorial seems to have some success. Check out "programming an Arduino with another".</p>
