SRI2K datasheet(24/45 Pages) STMICROELECTRONICS

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Anticollision

SRI2K

24/45

Doc ID 15779 Rev 3

7.1

Description of an anticollision sequence

The anticollision sequence is initiated by the Initiate() command which triggers all the SRI2K

devices that are present in the reader field range, and that are in Inventory state. Only

SRI2K devices in Inventory state will respond to the Pcall16() and Slot_marker(SN)

anticollision commands.

A new SRI2K introduced in the field range during the anticollision sequence will not be taken

into account as it will not respond to the Pcall16() or Slot_marker(SN) command (Ready

state). To be considered during the anticollision sequence, it must have received the

Initiate() command and entered the Inventory state.

Table 4 shows the elements of a standard anticollision sequence. (See Figure 22 for an

example.)

After each Slot_marker() command, there may be several, one or no answers from the

SRI2K devices. The reader must handle all the cases and store all the Chip_IDs, correctly

decoded. At the end of the anticollision sequence, after Slot_marker(15), the reader can

start working with one SRI2K by issuing a Select() command containing the desired

Chip_ID. If a collision is detected during the anticollision sequence, the reader has to

generate a new sequence in order to identify all unidentified SRI2K devices in the field. The

anticollision sequence can stop when all SRI2K devices have been identified.

Table 4.

Standard anticollision sequence

Step 1

Init:

Send Initiate().

– If no answer is detected, go to step1.

– If only 1 answer is detected, select and access the SRI2K. After accessing the

SRI2K, deselect the tag and go to step1.

– If a collision (many answers) is detected, go to step2.

Step 2

Slot 0

Send Pcall16().

– If no answer or collision is detected, go to step3.

– If 1 answer is detected, store the Chip_ID, Send Select() and go to step3.

Step 3

Slot 1

Send Slot_marker(1).

– If no answer or collision is detected, go to step4.

– If 1 answer is detected, store the Chip_ID, Send Select() and go to step4.

Step 4

Slot 2

Send Slot_marker(2).

– If no answer or collision is detected, go to step5.

– If 1 answer is detected, store the Chip_ID, Send Select() and go to step5.

Step N

Slop N

Send Slot_marker(3 up to 14)...

– If no answer or collision is detected, go to stepN+1.

– If 1 answer is detected, store the Chip_ID, Send Select() and go to stepN+1.

Step 17

Slot 15

Send Slot_marker(15).

– If no answer or collision is detected, go to step18.

– If 1 answer is detected, store the Chip_ID, Send Select() and go to step18.

Step 18

All the slots have been generated and the Chip_ID values should be stored into

the reader memory. Issue the Select(Chip_ID) command and access each

identified SRI2K one by one. After accessing each SRI2K, switch them into

Deselected or Deactivated state, depending on the application needs.

– If collisions were detected between Step2 and Step17, go to Step2.

– If no collision was detected between Step2 and Step17, go to Step1.

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