LRI64 datasheet(25/52 Pages) STMICROELECTRONICS

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LRI64

Anti-collision

25/52

Anti-collision

The purpose of the anticollision sequence is to allow the VCD to compile a list of the LRI64

devices that are present in the VCD field, each one identified by its unique ID (UID).

The VCD is the master of the communication with one or multiple LRI64 devices. It initiates

the communication by issuing the Inventory request (Figure 22).

15.1

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.

15.2

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 20, 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-bit mask plus the

current slot number is compared to the UID.

15.3

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 definition of the EOF in ISO 15693 and ISO

18000-3 Mode 1 standards.

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