Moog Crossbow GNAV540 - Manual (Page 62)

Page 62
GNAV540 User Manual
7430‐0808‐01 Rev. B
Descriptor Description Size (bytes) Comment Range
F4 Floating Point 4 IEEE754 Single
ion Precis
‐1*2^127 to 2^127
SN String N ASCII
Packet Format
ll of the Input and Output packets, except the Ping command, conform to the following structure: A
0x5555 <2‐byte packet type (U2)> <payload byte‐length (U1)> <variable length payload> <2‐byte CRC (U2)>
The Ping Command does not require a CRC, so a GNAV540 unit can be pinged from a terminal emulator. To Ping a
GNAV540 unit, type the ASCII string ‘UUPK’. If properly connected, the GNAV540 unit will respond with ‘PK’. All
other communications with the GNAV540 unit require the 2‐byte CRC.
NOTE: A GNAV540 unit will also respond to a ping command using the full packet formation with payload 0 and
correctly calculated CRC. Example: 0x5555504B009ef4.
Packet Header
The packet header is always the bit pattern 0x5555.
Packet Type
The packet type is always two bytes long in unsigned short integer format. Most input and output packet types can
be interpreted as a pair of ASCII characters. As a semantic aid consider the following single character acronyms:
Table 13 Character Acronyms
Acronym Description
P Packet
F Fields: Refers to Fields which are settings or data contained in the unit
E EEPROM Refers to factory data stored in EEPROM
R Read: Reads default non‐volatile fields
G Get: Ge s current volatile fields or settings t
W Write: Writes default non‐volatile fields. These fields are stored in non‐volatile memory and
determine the unit’s behavior on power up. Modifying default fields take effect on the next power
up and thereafter.
S Set: Sets current volatile fields or settings. Modifying current fields will take effect immediately by
modifying internal RAM and are lost on a power cycle.