Hi Matthew,

Connecting RxD and TxD together to the I/O line will probably not work. The I/O line on the ISO7816 interface is open collector/drain and the TxD line is usually a push-pull output. What you need to do is connect the TxD through an inverter to a transistor/MOSFET. Connect the emitter/source to GND and the collector/drain to the I/O and provide a pull-up resistor of around 10 - 20 kOhm. The RxD line of your uC can be connected directly to I/O.

Your method of disabling the receive interrupt during transmission will work. The UART should indeed be set to Mode 3 and reception will be no problem.

When transmitting you have to remember, though, that the TI bit is set after the Parity bit has been sent, so you need to add a delay to account for the STOP bit. Also remember that some cards need a "guardtime" between two consecutive bytes, which requires an even longer delay.

Best regards,
Rob Klein.