MICRF302 datasheet(6/15 Pages) MICREL

6 / 15 page

Micrel, Inc.

MICRF302

October 2008

M9999-100908-A

Functional Description

Overview

The MICRF302 is an encoder that prepares data for

transmission across an RF link. It is a parallel encoder,

meaning that it provides multiple parallel inputs for

connection to low-cost push-button switches.

The MICRF302 encoder translates push button closures,

any combination of D0 to D3, into baseband packets

using a set of internal logic blocks, which we describe

here.

Please refer to the Functional Diagram while

reading the following paragraphs.

Switch Deglitch and Register

When a button is pushed, the switch input is deglitched

to remove transient pulses shorter than 8 ms. The state

of the buttons is frozen and registered prior to

transmission. If multiple buttons are pushed within one

deglitch/sample time, their active levels will all be

included in the transmitted data.

Power Management

Immediately after any switch closure, the MICRF302

wakes from its standby (low-power) state and asserts

the TXEN output to start the RF transmitter. The Power

Management circuitry keeps the MICRF302 active

during

packet

transmission,

then

supervises

the

transition back to the standby state.

Clock Oscillator

The on-chip, trimmed oscillator is started by the Power

Management logic after startup (button press). It times

all internal events and sets the bit rate of the baseband

data via the clock generator. The clock oscillator

maintains its set frequency with a tolerance of ±10%

over process, voltage, and temperature variations

PPROM Trim

The Poly-fuse Programmable Read-Only Memory stores

the MICRF302’s unique address (see the PPROM ID

block), as well as other necessary information.

Power-On Reset

This self-contained, on-chip reset generator manages

the behavior of the MICRF302 when power is initially

applied, for example when a battery is inserted into the

transmitter. The POR sequencer and PPROM control

logic powers up the PPROM, loads important information

into internal registers, powers down the PPROM, and

then puts the whole chip into its standby state, ready for

the first button push event.

Packet Multiplexor

The

packet

multiplexor

chooses

the

appropriate

information for the MICRF302 to build and transmit a

packet. Under direction of the encoder state machine,

packet generation, packet assembly logic, the packet

multiplexor serializes the entire packet.

The packet

consists of: preamble, dead time, sync field, address,

and data. The packet multiplexor feeds into CRC

generation and data mux sections.

CRF Generation

computes the industry-standard 8-bit CRC.

The data

mux chooses the right information to be sent to the

transmitter. The data mux also ensures that the DOUT

pin is inactive when no packet transmission is in

progress.

Inter-Packet Delay

Getting its timing information from the Clock Generator,

the inter-packet delay block inserts the correct delay

between the four packets in a set. After each inter-

packet delay, the packet is repeated, increasing the

probability

accurate

detection

the

receiver.

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