HCS370P datasheet(16/36 Pages) MICROCHIP

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HCS370

DS41111D-page 16

Preliminary

2002 Microchip Technology Inc.

5.0

SPECIAL FEATURES

5.1

Internal RC Oscillator

The HCS370 has an onboard RC oscillator that con-

trols all the logic output timing characteristics. The

oscillator frequency varies over temperature and volt-

age variances, but stays within ±10% of the tuned

value. All the timing values specified in this document

are subject to this oscillator variation.

5.2

RF Enable and PLL Interface

The RFEN pin will be driven high whenever data is

transmitted through the DATA pin.

The RFEN and DATA outputs also interface with RF

PLL’s. The PLL Interface Select (PLLSEL) configura-

tion option selects between ASK and FSK interfaces.

Figure 5-1 shows the startup sequence for both ASK

and FSK interface options. The RFEN signal will go low

at the end of the last code word, including the guard

time (TG). The power-up time (TPU) is the debounce

time plus the step-up regulator ramp up delay if the

Wait For Step-Up Regulator (WAIT) configuration

option is a ‘1’. The PLL step-up time (TPLL) is also used

to update the EEPROM counter.

FIGURE 5-1:

ASK/FSK INTERFACE

5.3

LED Output

The LED pin will be driven low while the HCS370 is

transmitting data. The LED On Time (TLEDON) can be

selected between 50 ms and 100 ms with the LED On

Time Select (LEDOS) configuration option. The LED

Off Time (TLEDOFF) is fixed at 500 ms. When the VDD

voltage drops below the selected VLOW trip point, the

LED will not blink unless the LED Blink (LEDBL) option

is set. If LEDBL is set and VDD is low, then the LED will

only flash once. Waveforms of the LED behavior are

shown in Figure 5-2.

For circuits with VDD greater than 3 volts, be sure to

limit the LED circuit with a series resistor. The LED out-

put can safely sink up to 25 mA but adding an external

resistor will conserve battery power. This is an open

drain output but it does have a weak pull-up capable of

driving a CMOS input.

ASK RFEN

ASK DATA

FSK RFEN

FSK DATA

TPU

TPLL

CODE WORD

VBAT

VREG

STEP

Wait 2 seconds for next

button if QUEN=1

SLEEP

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