M24LR04E-R datasheet(72/142 Pages) STMICROELECTRONICS

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Anticollision

M24LR04E-R

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Doc ID 022208 Rev 5

Anticollision

The purpose of the anticollision sequence is to inventory the M24LR04E-Rs present in the

VCD field using their unique ID (UID).

The VCD is the master of communications with one or several M24LR04E-Rs. It initiates

M24LR04E-R communication by issuing the Inventory request.

The M24LR04E-R sends its response in the determined slot or does not respond.

21.1

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 are 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 provided in Table 34 and Figure 50, 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 33.

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 34.

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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