MC13201 Technical Data, Rev. 1.3,
Freescale Semiconductor 5
4 Data Transfer Mode
The MC13201 has a data transfer mode called Packet Mode where data is buffered in on-chip Packet
RAMs. There is a TX Packet RAM and an RX Packet RAM, each of which are 64 locations by 16 bits
wide.
4.1 Packet Structure
Figure 3 shows the packet structure of the MC13201 which is consistent with the 802.15.4 Standard.
Payloads of up to 125 bytes are supported. The MC13201 adds a four-byte preamble, a one-byte Start of
Frame Delimiter (SFD), and a one-byte Frame Length Indicator (FLI) before the data. A Frame Check
Sequence (FCS) is calculated and appended to the end of the data.
Figure 3. MC13201 Packet Structure
4.2 Receive Path Description
In the receive signal path, the RF input is converted to low IF In-phase and Quadrature (I & Q) signals
through two down-conversion stages. A Clear Channel Assessment (CCA) can be performed based upon
the baseband energy integrated over a specific time interval. The digital backend performs Differential
Chip Detection (DCD), the correlator “de-spreads” the Direct Sequence Spread Spectrum (DSSS) Offset
QPSK (O-QPSK) signal, determines the symbols and packets, and detects the data.
The preamble, SFD, and FLI are parsed and used to detect the payload data and FCS which are stored in
RAM. A two-byte FCS is calculated on the received data and compared to the FCS value appended to the
transmitted data, which generates a Cyclical Redundancy Check (CRC) result. Link Quality is measured
over a 64 µs period after the packet preamble and stored in RAM.
The MC13201 uses a packet mode where the data is processed as an entire packet and stored in Rx Packet
RAM. The MCU is notified that an entire packet has been received via an interrupt.
Figure 4 shows CCA reported power level versus input power. Note that CCA reported power saturates at
about -57 dBm input power which is well above 802.15.4 Standard requirements. Figure 5 shows energy
detection/LQI reported level versus input power.
NOTE
For both graphs, the required 802.15.4 Standard accuracy and range limits
are shown. A 3.5 dBm offset has been programmed into the CCA reporting
level to center the level over temperature in the graphs.
Preamble SFD FLI Payload Data FCS
4 bytes 1 byte 1 byte 125 bytes maximum 2 bytes
