I do not think that it is a reliable solution to simply OR the RxD line of the MAX232 and the RxD line of the IRDA module together. There is no real guarentee that the port oppsite to the one of current interest may be doing some thing unexpected such as receiving something. Far better would be to put logic that specifically selects which RxD line to look at and have an output port line from the processor select which one.

The diode OR scheme will work for a quick prototype hack John...but I would never recommend it over using a small chip of the ilk that Erik recommended. The diode has the problem that you lose a whole 0.7 volts on either your low level noise margin or your high level noise margin, depending if you are trying to diode OR to a low level or diode or to a high level. An appropriate logic solution can be implemented for about 20 cents and will save you more than one irrate customer service call and/or more than one, in the field, fire brigade debugging session over the jul 4th holiday.

Michael Karas