Eurotech ZyWAN, Руководство пользователя

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PART 2: SOFTWARE CONFIGURATION
93 110150-1001F
The following table describes the fields of the position message.
FIELD BYTES DESCRIPTION
som 1 This field indicates the start of message and is always set to
0x7E.
snum 10 This field contains the unit serial number in ASCII left justified
and null(0) filled to the right.
npos 1 This field gives the number of positions in this message.
sval 1 The field contains the sequence value for each position
transmitted.
The sequence value for the first position transmitted is 0. The
sequence value is incremented by 1 for each subsequent
position transmitted. Since this value is only one byte, the
maximum sequence value is 255.
time 4 This field contains the UTC timestamp of the GPS position and
its value is in seconds since 1/1/1970.
stat 1 This field contains a code representing status of the position
from the GPS receiver. In addition, bits 5-7 are used as flags for
other conditions.
Status Codes:
Bit: 1 Condition: No response from GPS receiver
Bit: 2 Condition: Error in response from GPS receiver
Bit: 3 Condition: Almanac error response from GPS receiver
Bit: 4 Condition: Good position response from GSP receiver
Flag Bits:
Bit 5: UTC TIME FLAG – This bit must be set to indicate that the
TIMETAG represents UTC time.
Bit 6: OVERFLOW FLAG – This bit is set to indicate that this
position, after being added to the store and forward cache,
caused an existing position in the store and forward cache to be
deleted.
Bit 7: FIRST POSITION FLAG – This bit is set to indicate that
this is the first position to be transmitted after the device was
powered on. For all subsequent positions, this bit must be
cleared.
sats 1 This field contains the number of satellites currently being
tracked.
lat 4 This field contains the latitude of the position in 1/100,000
minutes. For example, the ‘North 26 Degrees 8.767840
Minutes’ is represented as (26 * 60 * 8.767840 *
100000) = 156876784.
lon 4 This field contains the longitude of the position in 1/100,000
minutes. For example, the ‘WEST 80 Degrees 15.222400
Minutes’ is represented as - (80 * 60 * 15.222400 *
100000) = - 481522240.
psrc 1 This field contains ASCII ‘G’(0x47) if this is a valid GPS position.
Otherwise, it contains ASCII ‘N’(0x4E).
speed 1 This field contains the speed in miles per hour.
head 2 This field contains the heading in degrees.