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Randy McNally GPS
How to get a Rand McNally GPS unit working with the WP.
The GPS receiver has 4 wires (Tx, Rx, GND, and +5V) and would otherwise
connect to a PC with RS232 serial ports. The WP serial ports are TTL. Rather
than using a Maxim part to convert the TTL to RS232 on the WP, then from rs232
to ttl on the GPS, bypass the TTL-> rs232 conversion all together.
This is the typical flow from PC to a serial device:
ttl -> rs-232 -> rs-232 -> ttl
Wire +5V, GND, Rx and Tx from CN15 on the WP to the 4 pins on the rj11 connector
on the back (You can do this, only if you don't need the modem.)
Then, tack on the 4 wires from a phone cable (with rj11 connector on one end)
onto the GPS receiver.
The GPS unit does not have a rs232 circuit driver, but rather transistors to
invert the voltages. So lift a pin on the transistor handling the Rx on the GPS
and connect Tx from the WP to it, then do the same with Tx on the GPS and Rx on
the WP. In the end, you have TTL from the CN15 going to TTL on the GPS.
After installing the Rand McNally software, hook the GPS receiver to
the phone jack on the back of the WP. The Rand McNally software detects the GPS
unit and after the 3-5 minutes it takes to locate and lock onto a satellite,
everything is up and running.
Note: RS232 enables you to run long distances of cable with no transmission
errors. The only draw back to this method is the limited distance of cable
between the GPS unit and the WP.