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LRI512 Datasheet(PDF) 24 Page - STMicroelectronics |
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LRI512 Datasheet(HTML) 24 Page - STMicroelectronics |
24 / 54 page LRI512 24/54 REQUEST PROCESSING BY THE LRI512 Upon reception of a valid Request, the LRI512 performs the following algorithm, where: – NbS is the total number of slots (1 or 16) – SN is the current slot number (0 to 15) – LSB (value, n) function returns the n least signif- icant bits of the value – MSB (value, n) function returns the n most sig- nificant bits of the value – “&” is the concatenation operator – Slot_Frame is either a SOF or an EOF SN = 0 if (Nb_slots_flag) then NbS = 1 SN_length = 0 endif else NbS = 16 SN_length = 4 endif label1: if LSB(UID, SN_length + Mask_length) = LSB(SN,SN_length)&LSB(Mask,Mask_length) then answer to inventory request endif wait (Slot_Frame) if Slot_Frame = SOF then Stop Anticollision decode/process request exit endif if Slot_Frame = EOF if SN < NbS-1 thenSN = SN + 1 goto label1 exit endif endif EXPLANATION OF THE POSSIBLE CASES Figure 32 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. – LRI512 #1 transmits its Response in Slot 0. It is the only one to do so, therefore no collision oc- curs and its UID is received and registered by the VCD; – The VCD sends an EOF, meaning to switch to the next slot. – In slot 1, two LRI512s, #2 and #3, transmit their Responses. This generates a collision. The VCD records it, and remembers that a collision was detected in Slot 1. – The VCD sends an EOF, meaning to switch to the next slot. – In Slot 2, no LRI512 transmits a Response. Therefore the VCD does not detect a LRI512 SOF and decides to switch to the next slot by sending an EOF. – In slot 3, there is another collision caused by Responses from LRI512 #4 and #5 – The VCD then decides to send a Request (for instance a Read Block) to LRI512 #1, whose UID was already correctly received. – All LRI512s detect a SOF and exit the anti-colli- sion sequence. They process this Request and since the Request is addressed to LRI512 #1, only LRI512 #1 transmits its Response. – All LRI512s are ready to receive another Re- quest. If it is an Inventory command, the slot numbering sequence restarts from 0. Note: the decision to interrupt the anti-collision se- quence is up to the VCD. It could have continued to send EOFs until Slot 15 and then send the Re- quest to LRI512 #1. |
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