Here's another one from VK3YY that got posted recently:
Good detailed blog post Reverse Engineering the Yaesu VX-8DR GPS Interface. From Feb. 2013. He didn't arrive at the solution, which I believe F4FXL and at least one other have. But I think he's got most of the relevant details for the padding differences listed as well as some other very useful info including details on the GPS chips used in VX-8 and VX-8G.
We now know how to connect to and send a properly formatted GPS NMEA message to the Yaesu VX-8DR. Here's the summary:
- 9600baud TTL 3.3V serial signalling, 8/N/1
- NOT RS232 -5 to +5V signalling -- you need a level converter if that's all you have
- 3-wire physical interface to the following pins:
Pin GPS Side Purpose Yaesu Side Purpose 4 GPS RX Yaesu TX 5 GPS TX Yaesu RX 6 GPS GND Yaesu GND
- According to 4Z7DTF (2016-01-15), there is no need for the communication to be bidirectional. Only the TX Data from the GPS to the VX-8 is required.
The messages need to be formatted exactly as follows: