Users must calibrate the Timble Bison DR + GNSS receiver after installation to ensure an accurate output from the receiver. This must only be completed once. The Bison module can also be mounted in any arbitrary orientation and set to calibrate itself by using measurements made while the vehicle is moving to determine its actual orientation angles. It appears there is nothing needed from the processor other than the standard speed pulse and direction as in normal operation. But there is also the option to send mounting angle configuration information. It is a 38-byte HIPPO message to Set and a 70-byte Query over UART, plus 6 framing bytes. The overall HIPPO (derived from TSIP) message rate is 10 Hz, with a max size of 128 bytes.

NMEA standard is 4800 bps, 8 data bits word, and messages sent one per second. This is just enough throughput for the 6 different standard GPS messages (with a max size of 81 bytes) to come through in one second. 81*8*6 = 3888.

NMEA vs HIPPO, Trimble Bison

By default, the module outputs HIPPO. Using commands, you can enable NMEA and have both protocols output or select NMEA only.

HIPPO is a rich protocol that provides a lot of diagnostic value. We can also replay HIPPO logs through a post-processing tool called Bloodhound which allows us to remotely diagnose problems in the system. For example, missing wheel ticks. Most of our automotive OEM customers use HIPPO.

Non-automotive customers tend to use NMEA, since it is directly supported by most mapping software. It's easier to parse and will put a dot on a map, but it has limited diagnostic value.

Through commands, you can select the protocol desired and save to flash for the next power cycle. However, if you want NMEA by default right out of the box, then we should configure for NMEA.

Did you build in the ability to re-flash the BisonIII firmware from your host application? This is extremely handy in production-grade systems, since it allows you to update software without physically touching the module.