LRIS2K_08 datasheet(50/102 Pages) STMICROELECTRONICS

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Explanation of the possible cases

LRIS2K

50/102

Explanation of the possible cases

Figure 40 summarizes the main possible cases that can occur during an anticollision

sequence when the slot number is 16.

The different steps are:

●

The VCD sends an Inventory request, in a frame terminated by an EOF. The number of

slots is 16.

●

LRIS2K 1 transmits its request in Slot 0. It is the only one to do so, therefore no collision

occurs and its UID is received and registered by the VCD;

●

The VCD sends an EOF in order to switch to the next slot.

●

In slot 1, two LRIS2Ks, LRIS2K 2 and LRIS2K 3 transmit a request, thus generating a

collision. The VCD records the event and remembers that a collision was detected in

Slot 1.

●

The VCD sends an EOF in order to switch to the next slot.

●

In Slot 2, no LRIS2K transmits a request. Therefore the VCD does not detect any

LRIS2K SOF and decides to switch to the next slot by sending an EOF.

●

In slot 3, there is another collision caused by requests from LRIS2K 4 and LRIS2K 5

●

The VCD then decides to send a request (for instance a Read Block) to LRIS2K 1

whose UID has already been correctly received.

●

All LRIS2Ks detect an SOF and exit the anticollision sequence. They process this

request and since the request is addressed to LRIS2K 1, only LRIS2K 1 transmits a

request.

●

All LRIS2Ks are ready to receive another request. If it is an Inventory command, the

slot numbering sequence restarts from 0.

Note:

The decision to interrupt the anticollision sequence is made by the VCD. It could have

continued to send EOFs until Slot 16 and only then sent the request to LRIS2K 1.

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