Globalstar SmartOne - Manual (Page 70)

SmartOne Manual Rev 1.4 DOC# 9100-0268-01 p.70
AA 05 27 <CRC-low> <CRC-high>
What actually goes out over the air is:
12 22 33 44 55 66 77 88 99
Another example, using a longer message as supported by firmware version 2.1 and higher:
The Host sends:
AA 21 27 10 22 33 44 55 66 77 88 99 AA BB CC DD EE FF 11 22 33 44 55 66 77 88 99 AA 44 56 78 <CRC-low>
<CRC-high>
Note the length field, the command contains a total of 33 bytes. The length is 21 Hexadecimal, which is equal to 33
decimal.
The SmartOne Responds:
AA 05 27 <CRC-low> <CRC-high>
What actually goes out over the air is:
12 22 33 44 55 66 77 88 99 AA BB CC DD EE FF 11 22 33 44 55 66 77 88 99 AA 44 56 78 00 00 00 00 00 00 00
00
Note that all on air messages are padded to a multiple of 9 bytes. This is the reason for the trailing zeros in this
example.
Note that the least two significant bits of the first byte are always “10” for a raw message (a HEX or decimal value
of “2”, the remaining 6 bits make up the top 6 bits of the first byte sent in the serial command, in this example
000100xx (with the “xx” representing the two bits that the SmartOne forces to “10”.
A simple ACK or NAK from the SMARTONE Device to the host (smart sensor):
ACKs:
AA 05 26 <crc crc> (for the Truncated message)
AA 05 27 <crc crc> (for the Raw message)
NAK:
AA 05 FF <crc crc> (NAK).
Notes:
As the SmartOne operates, some debugging traces come out of the serial port. Those traces should simply be
ignored. Once the handshake line is pulled low, the unit is in “command mode” and debugging traces will stop.
User commands will ALWAYS be responded to immediately with either an acknowledgement or a NAK (as shown
in the examples above). Once an acknowledgement (or NAK) is received, the host should simply ignore the serial
port until the next time it sends a command.
The most common reasons for a NAK are incorrect CRC, incorrect length field, or incorrect command field (i.e. not
0x26 or 0x27 for trunc and raw respectively).
The handshake line should be pulled low before sending each serial message. The recommended use of the
handshake line is: