The GPS in its simplest form is a receive only 4800bps stream.
Connect it to a pin, and use a timer to trigger an interrupt at
24,000Hz.  Inside the interrupt do a very simple serial receive
bit-shift operation:

Wait for the start bit (signal goes low) then wait two interrupts.
Every 5th interrupt take the current level of the pin, and shift it
into your receive register.
Do that 8 times, then check for a valid frame bit by making sure the
9th bit is high.
Go back to waiting for a start bit.

It's actually quite simple, and while you could make it more complex I
doubt you'll need to due to the proximity and signal quality of the
GPS receiver's data stream.

Put the modem on the real UART - you'll need all the error checking
and buffering you can get.

-Adam

On 4/19/07, Srinil <srinil@katuns.org> wrote:
>
> Hi,
>        I am using pic18f452, and i am trying retrieve data from gps reciever
> and then send data using gsm
>
> network,  but how i can connect both gps and gsm to pic18f452 (serial
> connection), so that the
>
> trasmission and reception is done simultaneously  (for real time
> application).
> --
> View this message in context: http://www.nabble.com/gsm%2Bgps%2Bpic-connection-tf3606129.html#a10075073
> Sent from the PIC - [PIC] mailing list archive at Nabble.com.
>
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