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CC2420
SWRS041B Page 32 of 89
CSn
SI
ADDR
ADDR
DATA
8MSB
DATA
8LSB
DATA
ADDR+1
SO
ADDR
TXFIFO
DATA
ADDR
DATA
ADDR+2
Status
Status
-
-
Status
Status
Status
Status
Command
Strobe
Register
Read
TXFIFO
Write
Figure 11. Multiple SPI Access Example
14 Microcontroller Interface and Pin Description
When used in a typical system,
CC2420
will
interface to a microcontroller. This
microcontroller must be able to:
•
Program
CC2420
into different modes,
read and write buffered data, and read
back status information via the 4-wire
SPI-bus configuration interface (
SI
,
SO
,
SCLK
and
CSn
).
•
Interface to the receive and transmit
FIFOs using the
FIFO
and
FIFOP
status pins.
•
Interface to the
CCA
pin for clear
channel assessment.
•
Interface to the
SFD
pin for timing
information (particularly for beaconing
networks).
14.1 Configuration
interface
A
CC2420
to microcontroller interface
example is shown in Figure 12. The
microcontroller uses 4 I/O pins for the SPI
configuration interface (
SI
,
SO
,
SCLK
and
CSn
).
SO
should be connected to an input
at the microcontroller.
SI
,
SCLK
and
CSn
must be microcontroller outputs.
Preferably the microcontroller should have
a hardware SPI interface.
The microcontroller pins connected to
SI
,
SO
and
SCLK
can be shared with other
SPI-interface devices.
SO
is a high
impedance output as long as
CSn
is not
activated (active low).
CSn
should have an external pull-up
resistor or be set to a high level when the
voltage regulator is turned off in order to
prevent the input from floating.
SI
and
SCLK
should be set to a defined level to
prevent the inputs from floating.
CC2420
µ
C
CSn
SI
SO
SCLK
MOSI
MISO
SCLK
GIO2
FIFO
FIFOP
CCA
SFD
GIO0
Interrupt
GIO1
Timer Capture
Figure 12. Microcontroller interface example