LRI64 datasheet(17/38 Pages) STMICROELECTRONICS

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LRI64

REQUEST PROCESSING BY THE LRI64

Upon reception of a valid Request, the LRI64 per-

forms the following algorithm, where:

–

NbS is the total number of slots (1 or 16)

–

SN is the current slot number (0 to 15)

–

The function LSB(value,n) returns the n least

significant bits of value

–

The function MSB(value,n) returns the n most

significant bits of 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 22. summarizes the main possible cases

that can occur during an anti-collision sequence

when the number of slots is 16.

The different steps are:

–

The VCD sends an Inventory Request, in a

frame, terminated by a EOF. The number of

slots is 16.

–

LRI64 #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, to switch to the next

slot.

–

In slot 1, two LRI64 devices, #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, to switch to the next

slot.

–

In Slot 2, no LRI64 transmits a Response.

Therefore the VCD does not detect a LRI64

SOF, and decides to switch to the next slot by

sending an EOF.

–

In slot 3, there is another collision caused by

Responses from LRI64 #4 and #5

–

The VCD then decides to send a Request (for

instance a Read Block) to LRI64 #1, whose

UID was already correctly received.

–

All LRI64 devices detect a SOF and exit the

anti-collision sequence. They process this

Request and since the Request is addressed

to LRI64 #1, only LRI64 #1 transmits its

Response.

–

All LRI64 devices 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 se-

quence is up to the VCD. It could have continued

to send EOFs until Slot 15 and then send the Re-

quest to LRI64 #1.

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