LRI2K datasheet(39/89 Pages) STMICROELECTRONICS

39 / 89 page

LRI2K

Anti-collision

39/89

Anti-collision

The purpose of the anti-collision sequence is to inventory the LRI2Ks present in the VCD

field using their unique ID (UID).

The VCD is the master of communications with one or several LRI2Ks. It initiates LRI2K

communication by issuing the Inventory request.

The LRI2K sends its response in the determined slot or does not respond.

15.1

Request parameters

When issuing the Inventory command, the VCD:

●

sets the Nb_slots_flag as desired,

●

adds the Mask Length and the Mask Value after the Command Field,

The Mask Length is the number of significant bits of the Mask Value.

The Mask Value is contained in an integer number of bytes. The Mask Length indicates the

number of significant bits. The LSB is transmitted first.

If the Mask Length is not a multiple of 8 (bits), as many 0-bits as required will be added to

the Mask Value MSB so that the Mask Value is contained in an integer number of bytes.

The next field starts on the next byte boundary.

In the example of Table 18 and Figure 39, the Mask Length is 11 bits. Five 0-bits are added

to the Mask Value MSB. The 11-bit Mask and the current slot number are compared to the

UID.

Table 17.

Inventory request format

MSB

LSB

SOF

Request_

flags

Command

Optional AFI

Mask

length

Mask value

CRC

EOF

8 bits

0 to 8 bytes

16 bits

Table 18.

Example of the addition of 0-bits to an 11-bit mask value

(b15) MSB

LSB (b0)

0000 0

100 1100 1111

0-bits added

11-bit Mask Value

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