HCS473-SLROM datasheet(11/68 Pages) MICROCHIP

11 / 68 page

 2002 Microchip Technology Inc.

Preliminary

DS40035C-page 9

HCS473

2.3.5

INTERNAL RC OSCILLATOR

The HCS473 runs on an internal RC oscillator. The

internal oscillator may vary ±10% over the device’s

rated voltage and temperature range for commercial

temperature devices. A certain percentage of indus-

trial temperature devices vary further on the slow side,

-20%, when used at higher voltages (V

DD > 3.5V) and

cold temperature. The LF and RF communication

timing values are subject to these variations.

2.3.6

LOW VOLTAGE DETECTOR

The HCS473’s battery voltage detector detects when

the supply voltage drops below a predetermined value.

The value is selected by the Low Voltage Trip Point

Select (VLOWSEL) configuration option (Section 3.3).

The low voltage detector result is included in encoder

transmissions (VLOW) allowing the receiver to indicate

when the transmitter battery is low (Section 3.1.4.6).

The HCS473 also indicates a low battery condition by

changing the LED operation (Section 3.1.5).

2.3.7

THE S3/RFEN PIN

The S3/RFEN pin may be used as a button input or RF

enable output to a compatible PLL. Select between S3

button input and RFEN functionality with the RFEN

configuration option (Table 2-2).

TABLE 2-2:

RFEN OPTION

RFEN

Resulting S3/RFEN Configuration

S3 button input pin with Schmitt Trigger

detector and internal pull-down resistor.

RFEN output driver.

S3 may not be used as a button input if the

RFEN option is enabled

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