LRI2K datasheet(42/89 Pages) STMICROELECTRONICS

42 / 89 page

Explanation of the possible cases

LRI2K

42/89

Explanation of the possible cases

Figure 40 summarizes the main possible cases that can occur during an anti-collision

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.

●

LRI2K 1 transmits its response 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 LRI2Ks, LRI2K 2 and LRI2K 3 transmit a response, 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 LRI2K transmits a response. Therefore the VCD does not detect any

LRI2K SOF and decides to switch to the next slot by sending an EOF.

●

In slot 3, there is another collision caused by responses from LRI2K 4 and LRI2K 5

●

The VCD then decides to send a request (for instance a Read Block) to LRI2K 1 whose

UID has already been correctly received.

●

All LRI2Ks detect an SOF and exit the anti-collision sequence. They process this

request and since the request is addressed to LRI2K 1, only LRI2K 1 transmits a

response.

●

All LRI2Ks 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 anti-collision sequence is made by the VCD. It could have

continued to send EOFs until Slot 16 and only then sent the request to LRI2K 1.

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