I am pretty sure the Renasas part just sets up a standard "tickle me" for Flash config. During
power up sequencing it probably blits something out a port pin and IF it gets a response,
then switches to a Flash load mode. It was probably designed for JTAG and they just tacked
RS-232 level translators on the JTAG pins, and set up the handshake across RS-232, because
it was cheaper than a JTAG dongle.
USB is laughably overkill for loading 32K of Flash. But info tech is SO bloated nowadays they
need all that bandwidth for the 4 megabytes of handshaking needed to pass a 32K packet...
power up sequencing it probably blits something out a port pin and IF it gets a response,
then switches to a Flash load mode. It was probably designed for JTAG and they just tacked
RS-232 level translators on the JTAG pins, and set up the handshake across RS-232, because
it was cheaper than a JTAG dongle.
USB is laughably overkill for loading 32K of Flash. But info tech is SO bloated nowadays they
need all that bandwidth for the 4 megabytes of handshaking needed to pass a 32K packet...