sri4k STMicroelectronics, sri4k Datasheet - Page 23

• Manufacturer Part Number: sri4k
• Description: 13.56 Mhz Short-range Contactless Memory Chip With 4096-bit Eeprom And Anticollision Functions
• Manufacturer: STMicroelectronics

SRI4K
7
Anticollision
The SRI4K 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 SRI4K 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 SRI4K device(s). It initiates
the tag communication activity by issuing an INITIATE(), PCALL16() or SLOT_MARKER()
command to prompt the SRI4K to answer. During the anticollision sequence, it might hap-
pen that two or more SRI4K devices respond simultaneously, so causing a collision. The
command set allows the reader to handle the sequence, to separate SRI4K transmissions
into different time slots. Once the anticollision sequence has completed, SRI4K communica-
tion is fully under the control of the reader, allowing only one SRI4K to transmit at a time.
The Anticollision scheme is based on the definition of time slots during which the SRI4K
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 SRI4K answers after the command is issued. SRI4K devices are allowed to
answer only once during the anticollision sequence. Consequently, even if there are several
SRI4K devices present in the reader field, there will probably be a slot in which only one
SRI4K answers, allowing the reader to capture its Chip_ID. Using the Chip_ID, the reader
can then establish a communication channel with the identified SRI4K. The purpose of the
anticollision sequence is to allow the reader to select one SRI4K at a time.
The SRI4K 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 (
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. SRI4K Chip_ID description
Each time the SRI4K 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 SRI4K receives the
SLOT_MARKER(SN) command, it compares its CHIP_SLOT_NUMBER with the
SLOT_NUMBER parameter (SN). If they match, the SRI4K returns its Chip_ID as a
response to the command. If they do not, the SRI4K 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
b
0
to b
3
) of the Chip_ID are also known as the
b4
8-bit Chip_ID
b3
b
, the SRI4K returns its whole 8-bit
Section 5: SRI4K
b0 to b3: CHIP_SLOT_NUMBER
b2
operation:
b1
Anticollision
b0
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