User Manual

PLUS System Manual Reader Data Interface 59
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Figure 3-2: changeIp and solverIp Commands
3.4 Detailed Interface Description
At startup, the Reader listens for a connection on TCP port 11001. The Reader can be controlled by
sending ASCII commands over this socket. Also, at startup (and subsequently when no Tag
transmission has been heard within 10 seconds), the Reader broadcasts a discovery TOA packet to UDP
port 11000 to announce its presence. The discovery TOA packet is a special form of the TOA packet
with the Tag ID set to zero. Once the Reader has started, it will send a binary TOA packet to UDP port
11000 for each Tag transmission received. The formats of the binary UDP packet and the ASCII TCP
commands are discussed in this section.
3.4.1 TOA Packet Format
The packet format description below follows the commonly used TCP/IP convention of numbering the
most significant bit as bit 0 and the least significant bit as bit 31. Also, packets are transmitted in
network byte order, meaning the most significant byte (bits 0-7) is transmitted first, followed by the
byte at bits 8-15, then bits 16-23, and the least significant byte (bits 24-31) last. This means that on
little endian architectures, multi-byte values will need to be byte swapped before use.
The Reader sends a TOA packet each time it successfully receives a Tag transmission. These packets
are unicast to port 11000 at the location engine’s IP address. The TOA packet consists of 4 32-bit
words, as shown below.
0 15
16 31
Reader ID (bits 0-31)
Reader ID (bits32-47)
Version
BS
BN
Seq Num
M
A
Tag ID
Coarse TOA
Fine TOA
RSSI
T
RS
Preamble Cnt
Figure 3-3: TOA Packet Format