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Processing Data from the Reader

Autonomous Configuration Tool v1.0 User Guide 23

Message Types Sent By Reader

When operating in autonomous mode there are three different messages that the reader

will send: Tag Read Data, Temperature Status (acts as keep-alive in GPI triggered read

mode) and Read-cycle reset/Keep-alive. The message types can be differentiated by

their Data Length field.

These messages contain the following data:

Tag Read Data Message

Table 5: Tag Read Data Packet Format

Field Value Description

Header (Hdr) 0xFF Defines the start of the packet.

Data Length (Len) [1 byte] Defines the length, M, of the data field contained in the

packet. Length value will be 0x10 to 0xFE

OpCode 0x22 Autonomous reader message

Status Word 0x0000 Since Tag Read Data messages only occur with successful

tag reads the status for these should always be 0x0000

RFU [7 bytes] Reserved for future use. Data can be ignored

RSSI [1 byte] Return Signal Strength Indicator

Antenna ID [1 byte] Antenna ID, 4 MSBs for TX and 4 LSBs for RX

Frequency [3 bytes] Frequency in kHz at which the tag was read

Timestamp [4 bytes]

Millisecond offset from last

Read-Cycle Reset/Keep-Alive

when tag was read.

Phase [2 bytes] Phase of signal tag was read at (0-180)

Protocol ID 0x05 Protocol ID of tag read 0x05 = Gen2/ISO18000/6C

Embedded Tag

Data Length

[2 byte] Length, in bits, of the embbeded tag data read for this tag.

This value indicates how many bytes (ceiling[bits/8]), up to

32, will follow.

Example: if the value is 0x1D (29) then 4 bytes will follow:

29/4 = 3.625 -- ceiling(3.625) = 4.

Tag Data [N bytes] Number of bytes of tag data as specified in Tag Data Length

1 2 ... 18 19 20 21 22 23 24 25 26 27 28

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