CC2500 Datasheet, PDF (23/76 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transceiver

CC2500
11 Microcontroller Interface and Pin Configuration
In a typical system, CC2500 will interface to a
microcontroller. This microcontroller must be
able to:
• Program CC2500 into different modes,
• Read and write buffered data
• Read back status information via the 4-wire
SPI-bus configuration interface (SI, SO,
SCLK and CSn).
11.1 Configuration Interface
The microcontroller uses four I/O pins for the
SPI configuration interface (SI, SO, SCLK and
CSn). The SPI is described in Section 10 on
page 19.
11.2 General Control and Status Pins
The CC2500 has two dedicated configurable
pins and one shared pin that can output
internal status information useful for control
software. These pins can be used to generate
interrupts on the MCU. See Section 28 on
page 45 for more details on the signals that
can be programmed. The dedicated pins are
called GDO0 and GDO2. The shared pin is the
SO pin in the SPI interface. The default setting
for GDO1/SO is 3-state output. By selecting
any other of the programming options the
GDO1/SO pin will become a generic pin. When
CSn is low, the pin will always function as a
normal SO pin.
In the synchronous and asynchronous serial
modes, the GDO0 pin is used as a serial TX
data input pin while in transmit mode.
The GDO0 pin can also be used for an on-chip
analog temperature sensor. By measuring the
voltage on the GDO0 pin with an external ADC,
the temperature can be calculated.
Specifications for the temperature sensor are
found in Section 4.7 on page 12.
The temperature sensor output is only
available when the frequency synthesizer is
enabled (e.g. the MANCAL, FSTXON, RX and
TX states). It is necessary to write 0xBF to the
PTEST register to use the analog temperature
sensor in the IDLE state. Before leaving the
IDLE state, the PTEST register should be
restored to its default value (0x7F).
11.3 Optional Radio Control Feature
The CC2500 has an optional way of controlling
the radio, by reusing SI, SCLK and CSn from
the SPI interface. This feature allows for a
simple three-pin control of the major states of
the radio: SLEEP, IDLE, RX and TX.
This optional functionality is enabled with the
MCSM0.PIN_CTRL_EN configuration bit.
State changes are commanded as follows:
When CSn is high the SI and SCLK is set to
the desired state according to Table 18. When
CSn goes low the state of SI and SCLK is
latched and a command strobe is generated
internally according to the control coding. It is
only possible to change state with this
functionality. That means that for instance RX
will not be restarted if SI and SCLK are set to
RX and CSn toggles. When CSn is low the SI
and SCLK has normal SPI functionality.
All pin control command strobes are executed
immediately, except the SPWD strobe, which is
delayed until CSn goes high.
CSn
1
↓
↓
↓
↓
0
SCLK
X
0
0
1
1
SPI
mode
SI
X
0
1
0
1
SPI
mode
Function
Chip unaffected by
SCLK/SI
Generates SPWD strobe
Generates STX strobe
Generates SIDLE strobe
Generates SRX strobe
SPI mode (wakes up into
IDLE if in SLEEP/XOFF)
Table 18: Optional pin control coding
Preliminary Data Sheet (rev.1.1.) SWRS040
Page 23 of 77