CC2500 Datasheet, PDF (35/76 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transceiver

CC2500
19.1 Power-On Start-Up Sequence
When the power supply is turned on, the
system must be reset. One of the following two
sequences must be followed: Automatic
power-on reset (POR) or manual reset.
19.1.1 Automatic POR
A power-on reset circuit is included in the
CC2500. The minimum requirements stated in
Section 4.9 must be followed for the power-on
reset to function properly. The internal power-
up sequence is completed when CHIP_RDYn
goes low. CHIP_RDYn is observed on the SO
pin after CSn is pulled low. See Section 10.1
for more details on CHIP_RDYn.
19.1.2 Manual Reset
The other global reset possibility on CC2500 is
the SRES command strobe. By issuing this
strobe, all internal registers and states are set
to the default, idle state. The manual power-up
sequence is as follows (see Figure 12):
• Set SCLK=1 and SI=0, to avoid potential
problems with pin control mode (see
Section 11.3 on page 23).
• Strobe CSn low / high.
• Hold CSn high for at least 40 µs.
• Pull CSn low and wait for SO to go low
(CHIP_RDYn).
• Issue the SRES strobe on the SI line.
• When SO goes low again, reset is
complete and the chip is in the IDLE state.
40µs
CSn
SO
Unknown/ don't care
SRES done
Figure 12: Power-on reset with SRES
19.2 Crystal Control
The crystal oscillator (XOSC) is either
automatically controlled or always on, if
MCSM0.XOSC_FORCE_ON is set.
In the automatic mode, the XOSC will be
turned off if the SXOFF or SPWD command
strobes are issued; the state machine then
goes to XOFF or SLEEP respectively. This
can only be done from the IDLE state. The
XOSC will be turned off when CSn is released
(goes high). The XOSC will be automatically
turned on again when CSn goes low. The state
machine will then go to the IDLE state. The SO
pin on the SPI interface must be zero before
the SPI interface is ready to be used; as
described in Section 19 on page 20.
If the XOSC is forced on, the crystal will
always stay on even in the SLEEP state.
Crystal oscillator start-up time depends on
crystal ESR and load capacitances. The
electrical specification for the crystal oscillator
can be found in Section 4.4 on page 10.
19.3 Voltage Regulator Control
The voltage regulator to the digital core is
controlled by the radio controller. When the
chip enters the SLEEP state, which is the state
with the lowest current consumption, this
regulator is disabled. This occurs after CSn is
released when a SPWD command strobe has
been sent on the SPI interface. The chip is
now in the SLEEP state. Setting CSn low again
will turn on the regulator and crystal oscillator
and make the chip enter the IDLE state.
When wake on radio is enabled, the WOR
module will control the voltage regulator as
described in Section 19.5.
19.4 Active Modes
CC2500 has two active modes: receive and
transmit. These modes are activated directly
by the MCU by using the SRX and STX
command strobes, or automatically by Wake
on Radio.
The frequency synthesizer must be calibrated
regularly. CC2500 has one manual calibration
option (using the SCAL strobe), and three
automatic calibration options, controlled by the
MCSM0.FS_AUTOCAL setting:
• Calibrate when going from IDLE to
either RX or TX (or FSTXON)
• Calibrate when going from either RX
or TX to IDLE
• Calibrate every fourth time when going
from either RX or TX to IDLE
The calibration takes a constant number of
XOSC cycles (see Table 28 for timing details).
When RX is activated, the chip will remain in
receive mode until a packet is successfully
Preliminary Data Sheet (rev.1.1.) SWRS040
Page 35 of 77