tcbcats,

I've been down this route before.... its not easy using a single pic to capture dual serial inputs at the same time. I found it damn impossible.

As you know with NMEA talkers, they transmit data at different time intervals. I found some of the more up market GPS receivers allow you to define the transmit intervals of each string.

If you had two such GPS receivers, you could set the time intervals with a big enough delay so that they never transmitted at the same time.. but this could quicky change especially if some one else changed the timing, or added more strings to transmit.

Or you could do the opposite... decrease the transmit
delay and focus on alternating the reception of each input. Then you can be sure that if you miss a string.. you'll capture it again next time it gets transmitted.

Back to your original question about speed....

I found that the main limiting factor wasn't speed... but memory.

Some NMEA strings are very long and you have to work on the NMEA data one string at a time. (and this between reception of the next string!)

It all comes down to which NMEA stings you are wanting to capture and how many.

I don't recommend using the USART.

Good luck.