LRIS2K datasheet(47/102 Pages) STMICROELECTRONICS

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LRIS2K

Anticollision

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Anticollision

The purpose of the anticollision sequence is to inventory the LRIS2Ks present in the VCD

field using their unique ID (UID).

The VCD is the master of communications with one or several LRIS2Ks. It initiates LRIS2K

communication by issuing the Inventory request.

The LRIS2K sends its request in the determined slot or does not respond.

17.1

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. 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 at the next byte boundary.

In the example of the Table 25 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 24.

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 25.

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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