I'm trying to build a MON08 interface to program a 68HC908QB8, as per page 13 of this PDF:
Below is my schematic, from which I have created a PCB:
I cannot get the Freescale Bootload software to connect, irrespective of any combination of the two switches. It attempts to look for a reset ACK signal, but times out:
Granted this is ageing technology now, but do USB to RS-232 converters run on a different voltage to regular RS-232 interfaces? I believe RS-232 signals are +/-12V? This would determine some of the resistor values in the circuit. If this is the case, would it be worth trying a PCIe-based RS-232 interface?
Am I missing anything in my schematic, compared to the schematic in the PDF?