SRI4K-SBN181GE STMICROELECTRONICS [STMicroelectronics], SRI4K-SBN181GE Datasheet - Page 22

• Manufacturer Part Number: SRI4K-SBN181GE
• Description: 13.56 MHz short-range contactless memory chip with 4096-bit EEPROM and anticollision functions
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Anticollision
7
22/45
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 happen 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 communication 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
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
b
, the SRI4K returns its whole 8-bit Chip_ID in its
b3
Section 5: SRI4K
b0 to b3: Chip_slot_number
b2
operation:
b1
b0
ai07668b
SRI4K