Version 2 GPS software

Version 2 of the GPS had a new program, although some of the old software is still recognizable.

It first initializes the variables, and the LCD display. It also sets the serial port for 4800 bps communication, which is what is needed for the GPS module. This means output to the PC will also be in this speed. The LCD activation sequence is always the same, as the R/W line is pulled down, we need to have maximum delays (160uS and 5ms respectively). Finally the software displays a . on the display to indicate that something is happening.

During the start loop it reads from the GPS until a valid string is read. If the button is pressed during this time, it is remembered so that the location can be recorded.

During the main loop it continues to read from the GPS and makes sure that a valid sentence is stored separately for later recording. The SendString routine sends the GPS string from the sentence that is at location Number. This is used to display relevant information for each screen.

There are a number of states, that can be cycled through using the button. In one state it works normally, displaying the location and recording locations and pictures in case the camera triggers the flash port. In various other states different information is displayed. In the sending state it displays "Sending..." and sends the complete memory to the PC over the serial port.

Other routines handle the storing in external memory, the reading from external memory, the writing and reading from the serial port, and the recognizing of a valid sentence and skipping all the other information from the GPS module.

The detecting of the switches is done with a separate routine, which sets a flag when it happens. This routine is called as often as possible, to make sure no button presses are missed.