take from RX, send to TX

I am using a GPS reciever to take the positon, And this gps reciever sends the positon data in a sentence which starts with $GPRMC,1,,12,3,23,3. If I cannot know if 'G' has come or not, then I cant take the posisiton data. So I must compare 'G' with incoming messages. I am sure that it sends all the chars without any compare.

If I initialize the usart wrongly, I think it also shouldnt send the other chars. And Do you know the software Proteus. It can simulate the circuit. I connect gps reciever to com 1 and simulate the circuit. It works correctly. But with my pic17f877, it doesnt fo the compare

Are you sure it's actually working and your terminal is not just supplying the echo?

What happens if you precede the first TXsend with movlw '1' or whatever...

Best regards, Spehro Pefhany

You're using a 16F pic, this series does not have the BZ instruction. I have no idea why your compiler doesn't pick this out for you, but if it just ignores this instruction, All your code does it echo the character.

I heard from someone that mplap compiler automatically creates a btfss and goto command. And I tried if it does or doesnot working. It works.

The GPS receiver probably sends several different sentences, all starting with "$GP", so you should first look for a "$", as that will only occur at the start of the sentence. You can then ignore the "GP" talker ID, and look for the "RMC". If you don't find "RMC", discard characters til you see the next "$". (Of course, you have to get the receive routine working correctly before you have to worry about these details....)