MCP450P Microchip Technology, MCP450P Datasheet - Page 15

• Manufacturer Part Number: MCP450P
• Description: 13.56 MHz Read/Write Passive RFID Device
• Manufacturer: Microchip Technology

5.0
This section encodes data with the Manchester format
and also detects commands from the Interrogator.
5.1
This circuit demodulates the Interrogator commands
and sends them to the PPM decoder.
5.2
This oscillator generates a clock frequency that is used
for decoding Fast mode commands.
5.3
This section decodes the PPM signals and sends the
results to the command decoder and CRC/parity
checker.
5.4
This section decodes the Interrogator commands and
sends the results to the Anti-collision/command
controller.
5.5
This section generates Cyclic Redundancy Code
(CRC) and parity bits for transmitting and receiving
data. The device utilizes a 16-bit CRC for error
detection. Its polynomial and initial values are:
This polynomial is also known as CRC CCITT
(Consultative Committee for International Telegraph
and Telephone). The Interrogator also uses the same
CRC for data processing. The device uses the CRC in
the following ways:
1.
 2003 Microchip Technology Inc.
CRC Polynomial: X
Initial Value: $FFFF
CRC for blocks (except Blocks 0 and 2): The
Interrogator will send a Write command with
CRC. When the device receives this command,
it checks the CRC prior to any processing. If it is
a correct CRC, the device programs the block
data and also stores the CRC in the EEPROM.
As soon as the data is written into memory, both
the programmed data and Stored CRC (SCRC)
are sent back to the Interrogator as verification.
The device also sends the programmed data
and SCRC when there is a response to the
Read command.
If the CRC is incorrect, the device ignores the
incoming message (does not respond to the
Interrogator) and waits for the next command
with a correct CRC.
DETECTION AND ENCODING
Fast Mode Oscillator
PPM Signal Decoder
Command Decoder
CRC/Parity Generator and
Checker
Demodulator (Detector)
16
+X
12
+X
5
+X
0
MCRF450/451/452/455
2.
3.
5.6
This section multiplexes serial data, encodes it into
Manchester format and sends it to the modulation
circuit. See Figure 3-2 for the Manchester waveform.
CRC for Blocks 0 and 2: When reading Block
0 or 2, a Calculated CRC (CCRC) is sent. This
is because both the TF and FR bits in Block 0
are non write-protectable, while the rest of the
bits in the block are write-protectable. This
means the SCRC in the block no longer repre-
sents the CRC of the block data, if only the TF or
the FR bit is reprogrammed. This is also true for
Block 2, which is a write protection block. The
write-protected bit cannot be reprogrammed
once it has been written. Therefore, the SCRC in
Blocks 0 and 2 are not used. Instead, the device
calculates the current CRC of the block and
sends it to the Interrogator.
CRC for FRR response: For the Fast Read (FR)
response (this is the device response to an FRR
command), the CCRC of the tag ID and FRF
(Blocks 3-5) data is sent. The data length of the
FRF is determined by DF bits (see Table 7-6).
Data Encoder
DS40232H-page 15