How do I design my own on-board programmer using a serial port for Synergy MPUs?
You can refer to the below Renesas Flash Programmer sample circuit for programming by using a PC's serial port. This is in the process of being tested out and will be published in the Oct 2016 timeframe, but you can use the circuits and firmware in the below doc. The circuit "type C" is the currently recommended approach. Once published a new link will be added to this article.