LRI512 datasheet(24/54 Pages) 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

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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