You cannot do RS232 with the Measurement Computing PCI-DIO24. The PCI-DIO24 is strictly TTL level, which is not directly compatible with RS232. RS232 requires positive and negative voltages for signalling; TTL is positive voltages only.
You would need a USB to TTL device, and you would then have to wire through some of the pins to the 37 pin interface on the PCI-DIO24. You might perhaps want to wire through to the C port, as that 8 bit port can be split into two four bit ports, CH and CL. You would need to program your MCC driver to emulate RS232 asynch protocol (the protocols are the same, but the signal levels are different for the two.) See https://electronics.stackexchange.com/questions/6889/how-does-ttl-serial-work
I would suggest that you would need to have a special reason to bother using the MCC to emulate serial protocols instead of just tossing in a serial port or a USB port (if you do connect the USB, remember that USB is a master/slave protocol, so you typically cannot just connect two hosts directly together.)
