MCP2035-ISLASHST datasheet(44/68 Pages) MICROCHIP

44 / 68 page

MCP2035

DS22304A-page 44

 2012 Microchip Technology Inc.

Related Configuration register bits:

• Configuration Register 1 (Register 5-2),

DATOUT<8:7>:

bit 8 bit 7

: Demodulated Output

: Carrier Clock Output

: RSSI Output

• Configuration Register 2 (Register 5-3),

RSSIFET<8>:

: Pull-Down MOSFET off

: Pull-Down MOSFET on.

• Configuration Register 0 (Register 5-1): all bits

are affected.

FIGURE 5-8:

RSSI Output Path.

5.29.3.1

ANALOG-TO-DIGITAL DATA

CONVERSION OF RSSI SIGNAL

The RSSI output is an analog current. It needs an

external Analog-to-Digital (ADC) data conversion

device for digitized output. The ADC data conversion

can be accomplished by using a stand-alone external

ADC device, an external MCU that has internal ADC

features, or an external MCU that has no ADC features

but instead uses firmware. The RSSIFET is used to

discharge any external charge on the LFDATA pin in

the RSSI Output mode. The MOSFET can be turned on

or off with bit RSSIFET<8> of Configuration Register 2

(Register 5-3). When it is turned on, the internal

MOSFET provides a discharge path for the external

capacitor that is connected at the LFDATA pin. This

MOSFET option is valid only if RSSI output is selected

and not controllable by users for demodulated or carrier

clock output options.

See separate application notes for various external ADC

implementation methods for this device.

See Figure 5-8 for RSSI output path.

5.30

onfiguration Registers

5.30.1

SPI COMMUNICATION

The SPI communication is used to read from or write to

the Configuration registers and to send command-only

messages.

Three

pins

are

used

for

SPI

communication: CS, SCLK/ALERT, and LFDATA/RSSI/

CCLK/SDIO. Figure 5-9, Figure 5-10 and Figure 5-11

show examples of the SPI communication sequences.

When these pins are connected to the external MCU

I/O pins, the following are needed:

• Pin is permanently an input with an internal pull-up.

SCLK/ALERT

• Pin is an open collector output when CS is high.

An internal pull-up resistor exists to ensure no

spurious SPI communication between powering

and the MCU configuring its pins. This pin

becomes the SPI clock input when CS is low.

LFDATA/CCLK/SDIO

• Pin is a digital output (LFDATA) so long as CS is

high. During SPI communication, the pin is the

SPI data input (SDI) unless performing a register

Read, where it will be the SPI data output (SDO).

Note:

The pull-down MOSFET option is valid

only when the RSSI output is selected.

The MOSFET is not controllable by users

when demodulated or carrier clock output

option is selected.

RSSI Output Current

Generator

VDD

MOSFET (controlled

RSSI Pull-down

Current Output

LFDATA/CCLK Pin

RSSIFET(1)

Off

if RSSI active

RSSI Pin

Note 1:

The RSSIFET is used to discharge any

external capacitor that is connected at

the LFDATA pin.

by Config. 2, bit 8)

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