I have a project that involves upgrading an existing processor in several hundred pieces of equipment. I have designed a circuit board that is using a Teensy 3.6 as the brains. The processor is buried inside the equipment and the USB on the Teensy 3.6 is not easily accessible from the outside of the equipment case. In the future, the firmware on the Teensy will need to be upgraded as new features are added. There are several hundred of these units that will be upgraded with the Teensy processor boards and adding a USB port to the outside of the cases would cost thousands of dollars and much labor so it is not a viable option. The old processor is running a Rabbit 3400 and the firmware on it can be upgraded through an existing RS232 connection on the outside of the equipment case by using a serial download utility that loads the firmware via a UART on the Rabbit board.

The equipment case has an RS232 port and RS485 port on the outside of the case available. My question is: can the Teensy Loader program upload firmware to a Teensy board via a UART instead of the USB port? If not, is there any other programs out there that can do this? I realize there would have to be some code on the Teensy 3.6 as well to make this happen. Any help on this is greatly appreciated.