ZyWAN User Manual
Configuring the ZyWAN
© 2008 Arcom Issue D
79
Arcom format for GPS messages (UDP)
When using the
Arcom Format
for GPS data, the position message shall be transmitted
using the User Datagram Protocol (UDP). If caching is enabled, the ZyWAN waits a
minimum of 10 seconds to receive an acknowledgement message after transmission of
a position message. If a response message is received that does not contain the
characters
ACK
or no message is received within the timeout period, the position
message shall be retransmitted. This process shall continue indefinitely. The
ACK
should be 3 ASCII characters (0x41 0x43 0x4B).
The position message is defined below. The first 12 bytes are a header, followed by 19-
byte portions containing the timestamp and position information. The number of these
19-byte portions is determined by the
Send Threshold
parameter. All data shall be in
binary big-endian format, unless otherwise specified.
Message header:
som(1)
snum(10)
npos(1)
Position data (repeated):
sval(1)
time(4)
stat(1)
sats(1)
lat(4) lon(4) psrc(1)
speed(1) head(2)
Field
Bytes Description
som
1
Start of message indicator. Always set to 0x7E.
snum
10
Unit serial number in ASCII left justified and null(0) filled to the right.
npos
1
Number of positions in this message.
sval
1
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
UTC timestamp of the GPS position. This 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