AT24RF08C View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'AT24RF08C' PDF : 21 Pages View PDF
AT24RF08C
Serial EEPROM Exceptions
In general, the two-wire serial interface on the AT24RF08C
functions identically to the AT24C08. The following
exceptions exist, as noted elsewhere within this document.
• Pins 1, 2 and 3 have a different usage.
• Access to various blocks may be restricted via the
access protection circuitry.
• The two block address bits (B2 and B1) in the command
byte are ignored with all read commands. They are set
only via the write command.
• Multi-byte reads do not cross block boundaries, but
instead wrap to the beginning of the block.
• Operation of the serial bus at 400 kHz is not guaranteed.
• Maximum operating voltage is 5.5V, maximum operating
temperature is 85×C.
• The serial port will be reset whenever the PROT pin is
low.
• If a multi byte read is in progress when an RFID write
starts, all data will be read as all 1s.
• Under some circumstances, subsequent bytes within a
multi-byte read may have their data returned as all 1s to
the serial port if a read is simultaneously requested from
the RFID port.
• If more than 16 bytes are written to the EEPROM with a
page write, overlapping bytes will have their values
corrupted.
• If VCC is 0V, the device draws current on the SDA, SCL,
WP and PROT pins when they are brought above 0V.
RFID Port Operation
The AT24RF08C includes a powerful and flexible RFID
communications port that permits moving data into or out of
the device through a simple coil antenna. Features include
automatic serial number transmission as well as
commands for explicit reads and writes to specified
locations within the EEPROM. Special capability has been
added to permit a tag to be individually identified and
selected when it is within the field at the same time as the
other tags.
The general strategy for implementing multiple tags within
the field is as follows:
Upon power-up, the tag waits a random period of time and
then transmits, as a header, a fixed pattern that occupies
four bit times. The value of each half-bit time is fixed at the
pattern 01 11 11 10. (this is interpreted as one half-bit time
with no modulation, 3-bit times of modulation and another
half-bit time of no modulation).
Within the following listening window, the tag must receive
an acknowledge pulse from the reader. See the “Listening
Window” section for restrictions on this transmission.
If the tag does not see an acknowledge pulse during the
specific time within the listening window, but sees an
acknowledge pulse or command issued by the reader to
another tag, it goes into an infinite listening window until the
other tag is complete with its transaction.
If the tag does not see an acknowledge pulse or command
from the reader at any time, it will wait for a random length
of time before transmitting its four bit header again.
If it does receive this acknowledge pulse during the specific
time, then it will continuously transmit its complete ID
(defined below) with a three bit listening window between
frames, until a command is received from the reader.
After the ID has been properly received by the reader, the
tag will expect to receive a command from the reader
during the three bit listening window between ID frames.
One possible command is to set the QUIET bit, causing the
device to remain idle until the next power down or global
command. Remaining tags will then follow the same
procedure until each has its QUIET bit set.
ID Configuration
After the chip’s header field has been acknowledged, the
chip will transmit as its ID number, the first 12 EEPROM
bytes in the ID page, starting with byte 0. This transmission
will start 1664 ms after the end of the header transmission.
See “RFID Acknowledge Timing” on page 16.
This ID transmission will be preceded by a single start bit
that has a logical value of 1, and terminated by a single
stop bit that has a logical value of ‘0’. These start and stop
bits bracket each page or block of data transmitted by the
device as a result of a read or write command.
After transmission of the ID frame, the device will delay
transmission during a 3 bit listening window to listen for a
command to be initiated before repeating the ID
transmission again. Commands sent to selected tags must
be initiated during the tCDM1 interval within this listening
window, as per the “Listening Window” section on page 9.
If a write is taking place to the EEPROM from the serial
port, the device will transmit to the reader a logical 0 in
place of the ID value until that write completes. If a write
from the serial port has started before the command is
issued by the reader, then the command will be aborted
and the 4 bit header sent. If a serial port write starts after a
read command has commenced, then a 0 will be
transmitted to the reader during the time that the EEPROM
is busy with the write. In some cases, reads from the serial
port will also cause data to temporarily be read as 0’s.
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