190-00880-00
GPS 20x Technical Specifications
Rev. A
Page 14
APPENDIX B: GARMIN BINARY OUTPUT FORMAT
In Binary Output mode, GPS 20x will transmit packets once per second. The records must be enabled by commands
to the unit. Refer to the
Garmin Device Interface Specification
found in the Garmin Device Interface SDK
for
details on how to form and parse Garmin packets over USB. At the time of this printing, this document is located on
the Garmin Web site at:
www.garmin.com/support/commProtocol.html
. The ID of each command should be 10
decimal to signify that the record is a command. The data portion of the packet should be one of the following:
Function Command
(base
10)
Position Record On
49
Position Record Off
50
Note that the satellite data information is also enabled when the position record is enabled.
USB packets contain a header with a USB transport ID, a record ID, and the size of the record data in bytes.
Immediately following the header is the record data payload. Refer to the
Garmin Device Interface Specification
found in the Garmin Device Interface SDK for details on how to form and parse Garmin USB packets.
USB Packet:
- 0x## 0x00 0x00 0x00
(USB transport ID, 1 byte unsigned, 4 bytes reserved)
- 0x## 0x## 0x00 0x00
(Record ID, 2 bytes unsigned, 4 bytes reserved)
- 0x## 0x## 0x## 0x##
(Number of data bytes in record, 4 bytes unsigned)
- record data payload
All unused reserved bytes in the header must be zero.
The data bytes of each packet contain the record specified by the record ID. A description of each record follows.
