User Manual

60 Reader Data Interface PLUS System Manual
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Each field in the packet is discussed in detail below:
 Reader ID – The Reader’s 48-bit MAC address
 Version – 4-bit field that denotes the version of the data format. This document describes
version 2. Each time the format of the TOA packet changes, the version number will also
change.
 BS – 2-bit battery status reported by the Tag
 BN – 2-bit button event field from the Tag payload. A button event of 0 means that the button
is not pressed. A value of 1 indicates a single button push event. A value of 2 indicates that the
button was pressed twice. A value of 3 indicates a push-and-hold event (the button was
depressed for longer than 2 seconds).
 Sequence number – 6-bit sequence number from the Tag payload
 M – 1-bit motion detect field from the Tag payload. This field is currently not implemented.
 A – 1-bit alarm field that indicates the Reader has encountered an error condition. Additional
information can be found by querying the Reader’s alarm status and statistics.
 Tag ID – 32-bit ID of the transmitting Tag. This field will be zero for discovery packets.
 Coarse TOA – 8-bit field containing the coarse time-of-arrival value. Each bit represents 10 ns.
This field is undefined if field T below is 1.
 Fine TOA – 8-bit field containing the fine TOA value. Each bit represents 1/256 of a 10 ns
coarse interval. Thus, each bit is 39.0625 ps. This field is undefined if field T below is 1.
 RSSI – Received Signal Strength Indication. This 8-bit field is an estimate of the received
Tag’s signal strength. The minimum RSSI value is around 20, and the strongest compressed
signals peak at approximately 230.
 T – 1-bit field that indicates valid Coarse and Fine TOA values. A value of 0 indicates a valid
TOA. A value of 1 indicates an invalid TOA and the Coarse and Fine TOA fields are
undefined.
 RS – 2-bit field reserved for future use.
 Preamble Cnt – 5-bit field that indicates how many bits remained in the acquisition preamble
after the acquisition threshold was passed. Higher numbers indicate stronger signals. Valid
values range from 17-23.
An example structure declaration in the C programming language that would hold a TOA packet is as
follows:
struct toa
{
char readerId[6]; /* reader ID */
char versionBsBn; /* version, battery status, and button event */
char seqNumMA; /* sequence number, motion detect, and alarm */
int tagId; /* tag ID */
char coarseToa; /* coarse TOA value */
char fineToa; /* fine TOA value */
char rssi; /* received signal strength indicator */