When I opened the MX-500 I looked for a RS232 driver. There isn't one. I bussed the wires directly from the OSHUNG chip, through some ESD preotection diodes and resistors to the 7-pin connector. i looked at the states of the three signal lines in the connector, the ones labelled 40, 39 and 37 but I never saw them toggle. Their state were hi, lo and hi respectively if that tells you anything. I also tried looking around at micro-controllers in general to see if I could find one that had an LCD driver and a serial port on pins 40, 39 and 37. There were too many to sort through. I think some of the NEC line came close but that's not a firm memory.
Right now I'm still trying to get the download working. I am going through the support department of the USB chip company at present waiting to see if they can solve the problem. I had a big calamity tonight. I unwisely tried to program ALL. My MX-500 went through self test, passed it, turned on the light and promptly garbled all characters on nearly all screens. I think I overwrote the label page which contains URC labels as well as user programmed ones. I think I can restore it by borrowing the demo unit from the store and cloning all. The programming page works although no other does. I won't get back my original data until I can dowload the file stored on my PC. Now there's an incentive to complete the program:)
