Spatial FOG Reference Manual
Page 94 of 144
Version 2.3
03/05/2018
ANPP Header Format
Field
#
Bytes
Ofset
Data
Type
Size
Description
1
0
u8
1
Header LRC, see section 13.2.1
2
1
u8
1
Packet ID, see section 13.2.2
3
2
u8
1
Packet Length, see section 13.2.3
4
3
u16
2
CRC16, see section 13.2.4
Table 23: ANPP header format
13.2.1
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. The LRC can be found using the following:
LRC = ((pac packet_ crc[0] + crc[1])^0xFF) + 1
13.2.2
Packet ID
The packet ID is used to distinguish the contents of the packet. Packet IDs range from
0 to 255.
Within this range there are three diferent sub-ranges, these are system packets, state
packets and configuration packets.
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.
13.2.3
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.
13.2.4
CRC
The CRC is a CRC16-CCITT. The starting value is 0xFFFF. The CRC covers only the
packet data.
13.3
Packet Requests
Any packet can be requested at any time using the request packet. See section 13.8.2.
