Data Sheet

UM7 DATASHEET

Rev. 1.6 – Released 1/10/2016

by computers as well. The downside is that they are less efficient than binary packets, taking

more time to transmit the same amount of information.

Each NMEA packet begins with a $ symbol and ends with a carriage-return, linefeed pair (‘\r\n’,

simply a new line when viewed on a serial terminal). Between the start and end symbols, the

packet consists of a predefined comma-separated list containing sensor data.

NMEA packets can be automatically sent by the UM7 at between 1 Hz and 100 Hz. The actual

amount of data that can be transmitted depends on the baud rate, and some NMEA packets

(like the sensor data packet, for example) can quickly overwhelm the serial bus, preventing the

data from being transmitted as often as requested.

While NMEA messages can be transmitted by the UM7, the UM7 can only be configured using

binary packets – the UM7 transmits NMEA packets, but there are no NMEA packets defined to

change configuration settings.

Each NMEA sentence transmitted by the UM7 begins with the text sequence $PCHRx. The

character ‘P’ indicates that the packet to follow is a proprietary packet (i.e. it isn’t a standard

NMEA packet). The sequence ‘CHR’ indicates that it is a CH Robotics packet. Finally, the

character ‘x’ varies depending on the exact packet being transmitted.

Health Packet - $PCHRH

DESCRIPTION

The NMEA health packet contains a summary of health-related information, including basic GPS

information and sensor status information.

PACKET FORMAT

$PCHRH,time,sats_used,sats_in_view,HDOP,mode,COM,accel,gyro,mag,GPS,res,res,res,*checks

e.g. $PCHRH,105.015,05,11,1.5,0,0,0,0,0,0,0,0,0,*70

PACKET FIELD DESCRIPTION

Field

Description

$PCHRH

Header field, always precedes the health packet

time

e.g. 105.015

This field can be up to 13 digits long. There will always be three decimal digits.