CC2500_06 Datasheet, PDF (36/84 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transceiver

CC2500
CC2500 has a built-in state machine that is
used to switch between different operation
states (modes). The change of state is done
either by using command strobes or by
internal events such as TX FIFO underflow.
A simplified state diagram, together with
typical usage and current consumption, is
shown in Figure 5 on page 13. The complete
radio control state diagram is shown in Figure
15. The numbers refer to the state number
readable in the MARCSTATE status register.
This register is primarily for test purposes.
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.
When the CC2500 reset is completed the chip
will be in the IDLE state and the crystal
oscillator running. If the chip has had sufficient
time for the crystal oscillator and voltage
regulator to stabilize after the power-on-reset,
the SO pin will go low immediately after taking
CSn low. If CSn is taken low before reset is
completed the SO pin will first go high,
indicating that the crystal oscillator and voltage
regulator is not stabilized, before going low as
shown in Figure 16.
CSn
SO
XOSC and voltage
regulator stabilized
Figure 16: Power-on reset
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 17):
• 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 relative to
pulling CSn low
• 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.
XOSC and voltage regulator switched on
40 us
CSn
SO
XOSC and voltage
regulator stabilized
SI
SRES
Figure 17: Power-on reset with SRES
Note that the above reset procedure is only
required just after the power supply is first
turned on. If the user wants to reset the
CC2500 after this, it is only necessary to issue
an SRES command strobe.
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 10.1 on page 21.
PRELIMINARY Data Sheet (Rev.1.2) SWRS040A
Page 36 of 83