Texas Instruments CC2500 User Manual

CC2500
S
WRS040
C
Page
40
of
89
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
re
set 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
will be
running. If the chip has had
sufficient time for the crystal oscil
lator 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 is not stabilized, before going
low as
shown in
Figure
16
.
Figure
16
: Power
-
On R
eset
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
26
).

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
li
ne.

When
SO
goes low again, reset is
complete and the chip is in the IDLE state.
CS
n
SO
XOSC Stable
XOSC and voltage regulator switched on
S
I
SRES
40
us
Figure
17
: Power
-
O
n
R
eset with
SRES
Note
that
the above reset procedure is only
required just after
the power supply is first
turned on. I
f the user wants to reset the
CC2500
after this, it is only necessary to issue
a
n
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
pulled low
before the SPI interface is ready to be used;
as described in Section
10.1
on page
22
.
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
electric
al specification for the crystal oscillator
can be found in Section
4.4
on page
12
.
19.3
Voltage Regulator Control
The voltage regulator to the digital core is
controlled by the radio cont
roller. When the
chip enters the SLEEP state, which is the state
with the lowest current consumption,
the
voltage
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

Texas Instruments CC2500 Specifications

General

Brand	Texas Instruments
Model	CC2500
Category	Transceiver
Language	English