Correct errors in Mac OS X serial comms program

I've started a program using AMSerialPort. I need it to: 1. Open a serial port with user selected port, baud rate. Parity, stop bits, data bits are hard coded. 2. Write ASCII text commands, and read responses, if any. 3. Close the port (if open) when the program is closed, a new port is opened, or the close button is clicked. 4. Error checking and reporting. I'm a hobbyist, learning Cocoa.