ComLynx trivia

[+karri]

After my problems with the Osaka GPS I decided to make a little study of the Lynx serial port.

 

It is a fixed start bit, 8 bit (LSB first), parity, 1 stop bit.

 

But the parity bit can also be read directly from the control register as a 9th bit.

 

The 10th bit is also available as a framing-error status bit.

 

If the stop bit is a '1' then the system waits for the next start bit '0'.

 

If the stop bit is a '0' it flags a framing error and then next start depends on what happens next:

'0' '0' will trigger the reception of the next character immediately.

'0' '1' will enter the idle state waiting for the next start bit.

'1' enters the next the idle state to wait for the next character.

 

So after this little exercise I believe that it is possible to receive standard 8,n,1 GPS positional information by reassembling the data in software.

 

Receiving arbitrary data from a 8,n,1 source is not possible because the framing logic has so many different states that keep losing bits. But a clever algorithm should be able to match the bitstream to the NMEA data sent by a GPS mouse. They go for around USD 24 at ebay.

 

--

Karri

Edited September 23, 2007 by karri