KeithRB:
This does not sound like a "serial" display, you might want to check out these:
https://www.sparkfun.com/products/11441which you control by sending ASCII characters down the serial line.
I'm not sure what you mean there, they sound EXACTLY like serial displays to me. A 3-wire serial interface is a very common way of driving lots of digits and I've had good success with things like that using the ShiftOut function. Those sparkfun things are crap anyway. I bought one once, never again.