Reverse polarity in Direct serial data

I was struggling to get it right with direct serial data (no rs232 drivers etc).

One PIC, a 16F1827, was set to transmit RS-232 serial at TTL level and the bit 4 of BAUDCTL was set for this. The output drives a ASK little transmitter with appropriate data to keep the DC level somewhere in the middle, so the receiver's data slicer can extract the data.

The other PIC, a 16F886 was set to receive the data from the ASK receiver module and I was naive enough to trust that bit 4 of the famous BAUDCTL register was enough to get the job done.

Three days to discover the little detail in the data sheet, that this little bit 4 inverts ONLY the data to be transmitted and NOT the incoming to RX pin.

True, datasheet states that little phrase "transmit inverted data to RB7/TXCK pin" but was too careless to spot really see it. A simple inverter like a transistor or opamp will do the job but was happy to believe a bit 4 can save few parts here.

Hope this helps others on this pitfall.

Ioannis

If you have the pins available you could run the RX through the comparator to invert it.

Never thought of that! Very good idea. A little bit of rearranging might do it.

Thanks!

Ioannis