CC2550 Datasheet, PDF (24/50 Pages) Texas Instruments – Single Chip Low Cost Low Power RF-Transmitter

CC2550
sequences must be followed: Automatic
power-on reset or manual reset.
A power-on reset circuit is included in the
CC2550. The minimum requirements stated in
Section 11 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 17.1
for more details on CHIP_RDYn.
The other global reset possibility on CC2550 is
the SRES command strobe. By issuing this
strobe, all internal registers and states are set
to the default, idle state. The power-up
sequence is as follows (see Figure 11):
• Set SCLK=1 and SI=0.
• Strobe CSn low / high.
• Hold CSn high for at least 40µs.
• Pull CSn low and wait for SO to go low
(CHIP_RDYn).
• Issue the SRES strobe.
• 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 11: Power-up with SRES
It is recommended to always send a SRES
command strobe on the SPI interface after
power-on even though power-on reset is used.
23.2 Crystal Control
The crystal oscillator is automatically turned on
when CSn goes low. It 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 be done from
any 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 0 on page
14.
Crystal oscillator start-up time depends on
crystal ESR and load capacitances. The
electrical specification for the crystal oscillator
can be found in section 7 on page 7.
23.3 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.
On the CC2550, all register values (with the
exception of the MCSM0.PO_TIMEOUT field)
are lost in the SLEEP state. After the chip gets
back to the IDLE state, the registers will have
default (reset) contents and must be
reprogrammed over the SPI interface.
23.4 Active Mode
The active transmit mode is activated by the
MCU by using the STX command strobe.
The frequency synthesizer must be calibrated
regularly. CC2550 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 TX
(or FSTXON)
• Calibrate when going from TX to IDLE
• Calibrate every fourth time when going
from TX to IDLE
The calibration takes a constant number of
XOSC cycles (see Table 18 for timing details).
When TX is active, the chip will remain in the
TX state until the current packet has been
successfully transmitted. Then the state will
change as indicated by the
MCSM1.TXOFF_MODE setting. The possible
destinations are:
• IDLE
• FSTXON: Frequency synthesizer on
and ready at the TX frequency.
Activate TX with STX.
• TX: Start sending preambles
Preliminary Data Sheet (rev. 1.1) SWRS039
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