srt512 STMicroelectronics, srt512 Datasheet - Page 23

• Manufacturer Part Number: srt512
• Description: 13.56 Mhz Short-range Contactless Memory Chip With 512-bit Eeprom And Anticollision Functions
• Manufacturer: STMicroelectronics

SRT512
7
Anticollision
The SRT512 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 SRT512 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 SRT512 device(s). It
initiates the tag communication activity by issuing an INITIATE(), PCALL16() or
SLOT_MARKER() command to prompt the SRT512 to answer. During the anticollision
sequence, it might happen that two or more SRT512 devices respond simultaneously, so
causing a collision. The command set allows the reader to handle the sequence, to separate
SRT512 transmissions into different time slots. Once the anticollision sequence has
completed, SRT512 communication is fully under the control of the reader, allowing only one
SRT512 to transmit at a time.
The Anticollision scheme is based on the definition of time slots during which the SRT512
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 SRT512 answers after the command is issued. SRT512 devices are allowed to
answer only once during the anticollision sequence. Consequently, even if there are several
SRT512 devices present in the reader field, there will probably be a slot in which only one
SRT512 answers, allowing the reader to capture its Chip_ID. Using the Chip_ID, the reader
can then establish a communication channel with the identified SRT512. The purpose of the
anticollision sequence is to allow the reader to select one SRT512 at a time.
The SRT512 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 18. SRT512 Chip_ID Description
Each time the SRT512 receives a PCALL16() command, the CHIP_SLOT_NUMBER is
given a new 4-bit random value. If the new value is 0000
bit 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 SRT512 receives
the SLOT_MARKER(SN) command, it compares its CHIP_SLOT_NUMBER with the
SLOT_NUMBER parameter (SN). If they match, the SRT512 returns its Chip_ID as a
response to the command. If they do not, the SRT512 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
Section 5: SRT512
b0 to b3: CHIP_SLOT_NUMBER
b
, the SRT512 returns its whole 8-
b2
operation:
b1
Anticollision
b0
ai07668
23/49