Not able to communicate to MDC2230 via RS232

Hello, I am a student at Western Michigan University. My senior design group and I are using your MDC2230 to control the motors on our autonomous robot. We are trying to send commands to the motor controller from an STM32F429 microcontroller using UART to send and receive. The UART is setup with a baud rate of 115200 bits/s, 1 start bit, 1 stop bit, and no parity. The transmit pin of the microcontroller is connected to pin 3 of the serial port, the receive pin of the microcontroller is connected to pin 2 of the serial port, and the ground of the microcontroller is connected to pin 5 of the serial port. We have also added a 4.7K resistor and diodes to the receive line per the user manual as the microcontroller works on TTL voltage levels. We have set the motorcontroller's serial intervace to inverted mode by sending "setconfig(_RSBR, 5)" in the Roborun scripting tab. We have tried to send "!P 1 500_" from the microcontroller and have not gotten a response from the motor controller. The wheel doesn't turn and there is no echo or command acknowledgement/error character from the motor controller. We have verified that the data has been sent from the microcontroller and that no data is being sent from the motor controller by using an oscilloscope. Also, we are able to send and receive the "!P 1 500_ " command between two microcontrollers so we know the microcontroller code is correct. We are able to operate the motor controller using Roborun with no issues. Any information as to what we might be doing wrong or any suggestions as to what we can try to fix this problem would be greatly appreciated.

When you connect to the controller in Roborun+, what is the result of sending "?UID" in the console tab? It is possible that your controller is too old to be compatable with the diode circuit we outlined.

I Entered ?UID into the console and it returned with UID=300:1058:3014679:1261590280:540293169

I Entered ?UID into the console and it returned with UID=300:1058:3014679:1261590280:540293169

Hmm, It should work. Do you think you can post a picture of your wired circuit?