MICRF114 datasheet(10/34 Pages) MICROCHIP

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MICRF114

DS50002416A-page 10

Preliminary

 2015 Microchip Technology Inc.

Select the transmit frequency parameter to ensure that

the actual operating frequency, which is determined by

the selected crystal, falls into the frequency range

defined by the parameter. Refer to Table 2-2.

Equation 2-1 through Equation 2-1 show that the rest

of the programmable parameters can be calculated

from the Control bit fields.

EQUATION 2-1:

CRYSTAL LOAD

CAPACITOR

EQUATION 2-2:

RF TRANSMIT POWER

EQUATION 2-3:

RF OUTPUT TUNING

CAPACITOR

The operating frequency, the crystal load capacitor,

and the RF output tuning capacitor settings depend on

the selection of external components and, to a lesser

extent, PCB layout. If these parameters are different

from the default values, it must be set only once during

the first transmission after a POR event.

2.5

Transmitting

The MICRF114 is normally in Sleep mode. The MCU

always initiates entry into Transmit mode by sending a

Start bit, the compulsory Control bits, and the optional

Configuration bits to the MICRF114, which starts its

wake-up sequence. After the wake-up delay, it

transmits the data present on its SDI pin. The MCU

holds the SDI pin low for the maximum specified wake-

up time. If calibration is requested, the maximum

specified calibration time must be added to the wake-

up time.

Transmit parameters are not usually changed on the

fly, and recalibration is not necessary. Therefore, the

MCU can use the quick-start transmit sequence as

described in Section 2.3 “Communication with the

MCU”. However, except in the rare case that all default

parameter settings are acceptable for the application,

the first transmission after a POR event must include

sending the required Configuration bits. Recalibration

is always needed when the transmit frequency is in a

band that is different from the default value.

The MICRF114 stays in Transmit mode until the MCU

sends a Stop bit and then reverts to Sleep mode

without any time-out delay.

TABLE 2-2:

FREQUENCY RANGE

fTX range (MHz)

F<2:0>

Min

Max

285

305

325

345

365

385

405

425

445

Crystal Load Capacitor:

CXT = 7 pF + X <4:0> * 0.5 pF

RF Transmit Power:

PTX = -2 dBm + P <3:0> dBm

RF Output Tuning Capacitor:

CTX = 0 pF + R <3:0> * 0.2 pF

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