Is the CTS pin on the uart supposed to be the direct CTS pin state (translated from rs232 voltage as described below in a direct fashion through a voltage divider) or the inverted state (through a discrete voltage divder+inverter or an inverting receiver)? This makes a big difference. The datasheet should say.
-3 to -25VDC is MARK (OFF for control lines like CTS, for serial tx/rx this is the '1' state)
3 to 25VDC is SPACE (ON for control lines like CTS, for serial tx/rx this is the '0' state, and if held this way for more than 8/9 bit cycles counts as a serial BREAK))
MC1489 is an example of a quad rs232 receiver.
Last edited by Lord Nightmare; 06/02/16 05:05 PM. Reason: clarified