Are you sure? possible to check if the CIA is really dead or not?
The CIA has nothing to do with the serial data, in every Amiga the serial UART is in Paula. And this rarely has problems in this area. One of the CIAs does the I/O on the serial control lines, but you don't need them for slower serial speeds or very short transfers.
A basic serial port test is as simple as:
1. Run your favourite terminal emulator (e.g. Term), set flow control to disabled, set any serial speed you like (e.g. 9600 baud), disable local echo
2. Perform a serial loopback by shorting/linking only pins 2 and 3 (TX and RX data) on the serial port - same pins for either the DB9 connector on the PC or DB25 on the Amiga
3. Type anything on the keyboard, you should see it echoed on the terminal window and echo will stop when you remove the loopback
If that doesn't work, you've either got the wrong port selected (e.g. serial.device unit 0 on the Amiga, COM1 on the PC), or you may have a hardware fault. The common source of hardware problems would be the RS232 line drivers, the 1488 and 1489 in the Amiga. Also check the +12V and -12V supplies are present as the line drivers require both of these supplies.
If the loopback test is OK, then with the same serial settings, connect your null modem cable between machines. Serial speed will need to be the same on both machines (e.g. 9600 baud). If you type on one, it should display on the other terminal.
If that doesn't work, there's probably a cable problem. Ignoring flow control lines for now, you only need three wires for a basic null modem cable.
DB25 (Amiga) DB9 (PC)
Pin 2 ------------- Pin 2
Pin 3 ------------- Pin 3
Pin 5 ------------- Pin 5
If using a cable with 2 x DB9 connectors or 2 x DB25 connectors, then swap pins 2 and 3 at one end only.
So if that all works OK, enable hardware flow control [RTS/CTS] on *both* terminals and repeat the typing test. If that suddenly no longer works, there's possibly an issue with the hardware control lines (also driven by the Amiga 1488/1489). You need to use flow control with longer serial transfers and faster serial speeds else you're likely to get buffer over-run errors.
Also check the looping and connections on the hardware control lines in the null modem cable. I can't remember all the connection details, but there's plenty of websites with this
information.
