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Originally Posted by Joe Ross
Is it possible that what you are seeing is inverted from what you want? In the RS232 spec, 1 is -3 to -25 volts and 0 is +3 to +25 volts. However, for TTL serial ports there is no standard. In some +5v is 1 (as normal ttl) and in others 0v is 1 (taking the lower votage as 1, like RS232). Some microprocessors have settings for standard and inverted serial ports, I don't know if the PIC has that, or if the other device you are interfacing with does.
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We don't even have anything hooked up to the TTL port currently. We're just trying to understand why we're receiving stuff when it's unconnected. Noise or bleedover is the most likely cause, so we grounded the RX pin which should cancel anything like that out. However, even with the pin grounded, we still see data on the RX pin when watching it on the scope. Tomorrow we'll be trying it on our backup controller to see if the same condition exists on both or not.
Thanks anyway for the ideas, though...