sri512 STMicroelectronics, sri512 Datasheet - Page 24
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sri512
Manufacturer Part Number
sri512
Description
13.56-mhz Short-range Contactless Memory Chip With 512-bit Eeprom And Anti-collision Functions
Manufacturer
STMicroelectronics
Datasheet
1.SRI512.pdf
(50 pages)
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Anticollision
The SRI512 provides an anticollision mechanism that searches for the Chip_ID of each
device that is present in the reader field range. When known, the Chip_ID is used to select
an SRI512 individually, and access its memory. The anticollision sequence is managed by
the reader through a set of commands described in
The reader is the master of the communication with one or more SRI512 device(s). It
initiates the tag communication activity by issuing an INITIATE(), PCALL16() or
SLOT_MARKER() command to prompt the SRI512 to answer. During the anticollision
sequence, it might happen that two or more SRI512 devices respond simultaneously, so
causing a collision. The command set allows the reader to handle the sequence, to separate
SRI512 transmissions into different time slots. Once the anticollision sequence has
completed, SRI512 communication is fully under the control of the reader, allowing only one
SRI512 to transmit at a time.
The Anticollision scheme is based on the definition of time slots during which the SRI512
devices are invited to answer with minimum identification data: the Chip_ID. The number of
slots is fixed at 16 for the PCALL16() command. For the INITIATE() command, there is no
slot and the SRI512 answers after the command is issued. SRI512 devices are allowed to
answer only once during the anticollision sequence. Consequently, even if there are several
SRI512 devices present in the reader field, there will probably be a slot in which only one
SRI512 answers, allowing the reader to capture its Chip_ID. Using the Chip_ID, the reader
can then establish a communication channel with the identified SRI512. The purpose of the
anticollision sequence is to allow the reader to select one SRI512 at a time.
The SRI512 is given an 8-bit Chip_ID value used by the reader to select only one among up
to 256 tags present within its field range. The Chip_ID is initialized with a random value
during the READY state, or after an INITIATE() command in the INVENTORY state.
The four least significant bits (b
CHIP_SLOT_NUMBER. This 4-bit value is used by the PCALL16() and SLOT_MARKER()
commands during the anticollision sequence in the INVENTORY state.
Figure 20. SRI512 Chip_ID description
Each time the SRI512 receives a PCALL16() command, the CHIP_SLOT_NUMBER is given
a new 4-bit random value. If the new value is 0000
Chip_ID in its answer to the PCALL16() command. The PCALL16() command is also used
to define the slot number 0 of the anticollision sequence. When the SRI512 receives the
SLOT_MARKER(SN) command, it compares its CHIP_SLOT_NUMBER with the
SLOT_NUMBER parameter (SN). If they match, the SRI512 returns its Chip_ID as a
response to the command. If they do not, the SRI512 does not answer. The
SLOT_MARKER(SN) command is used to define all the anticollision slot numbers from 1 to
15.
b7
INITIATE()
PCALL16()
SLOT_MARKER().
b6
b5
0
to b
3
) of the Chip_ID are also known as the
b4
8-bit Chip_ID
b3
b
, the SRI512 returns its whole 8-bit
Section 5: SRI512
b0 to b3: CHIP_SLOT_NUMBER
b2
operation:
b1
b0
SRI512
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