NMEA checksum

I need to send a serial string to a GPS device. It needs to be followed by a crc two digit checksum which is an XORing of the data field. How would I do this without having to check it in advance? Using lookup and send them out one at a time after XORing with the previous?

Thanks,
Ron

Hi (again) Ron!

Do you need to change it in code? or are you just using it to send a command to change the default baud rate? i'm not sure how to do it in code, but i know the checksums for different bauds if it'll help ?