LRI64 datasheet(16/38 Pages) STMICROELECTRONICS

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LRI64

16/38

ANTI-COLLISION

The purpose of the anti-collision sequence is to al-

low the VCD to compile a list of the LRI64 devices

that are present in the VCD field, each one identi-

fied by its unique ID (UID).

The VCD is the master of the communication with

one or multiple LRI64 devices. It initiates the com-

munication by issuing the Inventory Request

(Figure 23.).

Request Flags

The Nb_slots_flag needs to be set appropriately.

The AFI Flag needs to be set, if the Optional AFI

Field is to be present.

Mask Length and Mask Value

The Mask Length defines the number of significant

bits in the Mask Value.

The Mask Value is contained in an integer number

of bytes.

The least significant bit of each is transmitted first.

If the Mask Length is not a multiple of 8 (bits), the

most significant end of the Mask Value is padded

with the required number of null bits (set to 0) so

that the Mask Value is contained in an integer

number of bytes, so that the next field (the 2-Byte

CRC) starts at the next byte boundary.

In the example of Figure 21., the Mask Length is

11 bits. The Mask Value, 10011001111, is padded

out at the most significant end with five bits set to

0. The 11 bits Mask plus the current slot number is

compared to the UID.

Inventory Responses

Each LRI64 sends its Response in a given time

slot, or else remains silent.

The first slot starts immediately after the reception

of the Request EOF.

To switch to the next slot, the VCD sends another

EOF.

The following rules and restrictions apply:

–

if no LRI64 answer is detected, the VCD may

switch to the next slot by sending an EOF

–

if one or more LRI64 answers are detected,

the VCD waits until the complete frame has

been received before sending an EOF, to

switch to the next slot.

The pulse shall be generated according to the def-

inition of the EOF in ISO 15693 and ISO 18000-3

Mode 1 standards.

Figure 21. Comparison between the Mask, Slot Number and UID

AI06682

Mask value received in the Inventory command

0000 0100 1100 1111 b 16 bits

The Mask value less the padding 0s is loaded

into the Tag comparator

100 1100 1111 b 11 bits

The Slot counter is calculated

xxxx

Nb_slots_flags = 0 (16 slots), Slot Counter is 4 bits

The Slot counter is concatened to the Mask value

xxxx 100 1100 1111 b

Nb_slots_flags = 0

15 bits

The concatenated result is compared with

the least significant bits of the Tag UID.

xxxx xxxx ..... xxxx xxxx x xxx xxxx xxxx xxxx

64 bits

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

b63

Compare

Bits ignored

UID

4 bits

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