Tom Handley wrote:
> I've had a DSO project on the `back burner' for a long time.
> I recently had a requirement to analyze IR remote signals so I'm going to
 finish the project.

IR carriers are only around 33-38kHz. IrDA is only 115 kBaud - 4 MBaud.
If you have some kind of ADC driven by your printer port, you could still have a
 very useful gadget with a HUGE
memory. Which you can program in C instead of PIC assembly.

> Both connect to a bidirectional PC parallel port.
> My design will be PIC-based and connect to the serial port.

I'd stick with parallel if I were you. You will appreciate it when you want to
 upload data into your PC.
And make sure you design for a commonly available cable such as the Laplink
 transfer cable.
This is only 4 data bits + 1 or 2 handshake bits in either direction.
It suits all printer ports, whereas an 8-bit interface might exclude itself from
 simpler PCs.
Either that or try using an LPT<->I2C interface.
This won't be slowed by baudrates, won't need a MAX232 chip, or the hassle of
 baud rate generation.
The PIC UARTs don't look very accurate at high speeds, while I2C doesn't need
 precise clocks.

I hear the very fastest scopes use a bit of co-ax cable as a delay line, and
 digitise signals from points along
it. but that's stretching a budget.