I have tested a proof of concept of driving a XL430 from the UART port of a RPi at 1Mbps.
The RPi has 2 UARTs: UART1 and mini UART. The mini UART isn’t stable at 1Mbps but the hardware of the UART1 is capable of much faster speeds than 1Mbps, the main limitation is the operating systems usage of the UART.
To get a stable 1Mbps from RPi UART I had to enable UART1 and increase the UART clock speed as the default clock speed is too low to generate UART at 1Mbps. I added the following 2 lines to the config.txt on RPi
I connected the RX pin of the RPi directly to the data line. The TX pin of the RPi will idle high so I connected the TX pin through a 4.7k resistor so that it will act as a pull up on the data line so that it can drive the data line but when the dynamixel transmits the dynamixel can sink to low against the pull up of the TX pin of the RPi. . This seemed to work really nicely as a converter from UART full duplex to half duplex. I connected the positive and negative of my Lipo 3S battery and also connected a common ground from the Lipo negative to the GND pin of the RPi.
I downloaded and installed the DynamixelSDK from Robotis github. I changed the baud rate to 1mbps and the port to the UART in read_write.py and ran the test script to test that the RPi could both transmit and receive to the dynamixel.