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Does anyone know how to monitor the external UART receive pin? thanks
Can you be more specific? are you talking about the UART on the 251 itself or the external UART on the development kit? What do you want to monitor?
Try a scope. Why do you want to monitor it? Do you doubt the data that you receive? For a 16550 type UART, you cannot monitor the state of the receive pin via a bit in some register of the UART, you can only do that with the other status lines.
i need to monitor the development kit's UART. I need to know when is data coming in. thanks
You haven't said what dev kit you're using! Have you looked at the schematic?
Usually the UART will generate an interrupt after you have received one byte (in case the FIFO is swicthed off) or after the FIFO has reached the limit that you have set or after data is waiting inside the FIFO for a certain time. Other than that, you might have to solve that problem in hardware and connect a free port pin to the serial input of the UART (Exactly there, not in front of the RS232 drivers, that would kill the processor, becauzse the voltage exceeds the maximum ratings of the port pin).