Wiring into M32C UART via Serial>USB. Boot Failed.

I am working on a car project with an M32C built into a radio. The radio board has a programming port for a 7-pin FFC cable. I have soldered on a 7-pin FFC top connector to the board, with a cable and adapter connected to a CP2102 TTL USB converter. According to the MCU manual, CLK needs to be pulled down with a resistor to 0v, CNVss pulled high with 5v, and the standard GND, Tx, & Rx. I have all these hooked up, with the CLK 0v tied into the same ground as the standard GND pin on the USB controller... I have used two types of USB adapters, and the drivers are all okay, but I cannot get the MCU flashing programming software to boot. I just get an Error: Boot Failed. Any advice? I'm pretty new to MCU wiring.