Hi All;
In my new project, i interfaced a Nokia 6110 Cell phone with 89C52. As you know, 89C52 has only one Uart, and so to communicate with PC and download user data, i needed a second Uart(chips have double uart are very expensive). So i wrote some codes for a half dublex uart which uses INT0 as RX. The sowtware Uart is communicating with 300 baud. I tested it for a long time, it seems to be ok. But now, when i connect it to the PC after a while (1-2 hours later) the controller is freezing!! Doing nothing! I changed the MAX 232 but it did the same thing. I measured the voltage of INT0, it was 5 volts, so the processor is not in a nested interrupt. I changed the xtal, whole reset circuitary of mcu but could not solve the problem. And i think the software is ok, because when i disconnect the system from PC there is no problem! Any suggestion
Regards.
EB