GPS Receiver Module and PIC18F2550

shezi

Hi!

I am doing my first project with microcontollers and I have PIC18F2550 and a Parallax GPS Module. I really want to ask a basic question of connection between the GPS and the Micro. There are four pins for the GPS: Vdd, GND, /RAW and SIO.

I want to know where to connect the SIO pin. The thing I am confused about is the micro (18f2550) has RX and TX pins (USART or UART??) and most GPS have those. But how would I connect "SIO" to both RX and TX for communication? OR do I just connect it to RX and leave TX?

Also, has anybody done a successful extraction of data after the hardware connection in C? Any exmaples will be helpful. Thanx

Leon

GPS module URL?

Leon

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Amateur radio callsign: G1HSM

Mike Green

You will probably have problems connecting the GPS Module to the 18F2550. It's possible to add external hardware to allow the RX and TX lines of the 18F2550 to share the connection to the SIO pin of the GPS module. This could be as simple as a two transistor open-collector buffer or an open collector non-inverting buffer on the TX line. I think the SIO pin already has a pullup, so you could just connect RX, SIO, and the open collector output together. Note that the header and command sent to the GPS Module will be echoed back to the 18F2550, so that needs to be accounted for.

It may be possible to connect these together without a buffer. It all depends on how you would enable and disable the TX output of the 18F2550. Best in this case would be to use a 1K resistor between the SIO pin of the GPS Module and the RX and TX pins of the 18F2550 to protect against damage from a possible short circuit if SIO and TX are both active at the same time and in opposite states (low / high).

Post Edited (Mike Green) : 1/23/2010 8:45:49 PM GMT