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 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.

●

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 anticollision 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 anticollision 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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