CC1100-RTR1 datasheet(43/100 Pages) TI1

43 / 100 page

CC1100

SWRS038D

Page 43 of 92

performance in TX and RX an alternative GDO

setting should be selected from the settings

found in Table 34 on page 56.

19.1.1 Automatic POR

A power-on reset circuit is included in the

CC1100. The minimum requirements stated in

Table 12 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

CC1100 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 oscillator 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 17.

Figure 17: Power-On Reset

19.1.2 Manual Reset

The other global reset possibility on

CC1100

uses 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

18):

•

Set SCLK = 1 and SI = 0, to avoid

potential problems with pin control mode

(see Section 11.3 on page 29).

•

Strobe CSn low / high.

•

Hold CSn high for at least 40µs 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.

CSn

XOSC Stable

XOSC and voltage regulator switched on

SRES

40 us

Figure 18: 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

CC1100

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

pulled low before the SPI interface is ready to

be used; as described in Section 10.1 on page

26.

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 14.

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, 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

CC1100-RTR1 Datasheet(PDF) 43 Page - Texas Instruments

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