Packet Requests; Packet Acknowledgement - Advanced Navigation Certus OEM Reference Manual

Certus Reference Manual • Advanced Navigation Packet Protocol
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Header
Header LRC
Table 37: ANPP Packet Structure
Field # Bytes Offset
1 0
2 1
3 2
4 3
Table 38: ANPP Header Format
10.1.1.1 Header LRC
The header LRC (Longitudinal Redundancy Check) provides error checking on the packet header. It also allows
the decoder to find the start of a packet by scanning for a valid LRC. Only the lower 8 bits of the calculation
below are provided in the LRC field of the packet header. The LRC can be found using the following:
10.1.1.2 Packet ID
The packet ID is used to distinguish the contents of the packet. Packet IDs range from 0 to 255. See
Advanced Navigation Packet
System packets have packet IDs in the range 0 to 19. These packets are implemented the same by every
device using ANPP.
State packets are packets that contain data that changes with time, i.e. temperature. State packets can be set
to output at a certain rate. State packets are packet IDs in the range 20 to 179.
Configuration packets are used for reading and writing device configuration. Configuration packets are packet
IDs in the range 180 to 255.
10.1.1.3 Packet Length
The packet length denotes the length of the packet data, i.e. from byte index 5 onwards inclusive. Packet length
has a range of 0 – 255.
10.1.1.4 CRC
The CRC is a CRC16-CCITT. The starting value is 0xFFFF. The CRC covers only the packet data.

10.1.2 Packet Requests

Any of the state and configuration packets can be requested at any time using the

10.1.3 Packet Acknowledgement

When configuration packets are sent to Certus, it will reply with an acknowledgement packet that indicates
whether the configuration change was successful or not. See
External data packets will also generate negative acknowledgement packets if there is a problem with the
packet. Positive acknowledgements will not be sent. See
v2.4
Packet ID Packet Length
Data Type
u8
u8
u8
u16
Protocol.
CRC16
Size
1
1
1
2
10.3.1 Acknowledge
9.5 External Data
Page 142
Packet Data
Description
Header LRC
Packet ID
Packet Length
CRC
10.3.2 Request
Packet.
for a list of External Data Packets.
10
Packet.
2024-12-17