5

Test bit D6 in the Periodic Flag Register

IFa1

go to 41 If this bit remains a 1 after 3 seconds

then abort and check hardware The crystal may be de-

fective or not installed There may be a short at OSC IN

is less than 10 MX

IFa0

then the oscillator is running go to step 7

6

Writea0tobit D6 in the Periodic Flag Register This

action puts the clock chip in the battery backed mode

This mode can be entered only if the OSC fail flag (bit

D6 of the Periodic Flag Register) is a 0 Reminder bit D6

is a dual function bit When read D6 returns oscillator

status When written D6 causes either the Battery

Backed Mode or the Single Supply Mode of operation

The only method to ensure the chip is in the battery

backed mode is to measure the waveform at the OSC

OUT pin If the battery backed mode was selected suc-

cessfully then the peak to peak waveform at OSC OUT

is referenced to the battery voltage If not in battery

measurement should be made with a high impedance

low capacitance probe (10 MX 10 pF oscilloscope

probe or better) Typical peak to peak swings are within

7

Writea1tobit D7 of Interrupt Control Register 1 This

action enables the PFAIL pin and associated circuitry

8

Writea1tobit D4 of the Real Time Mode Register This

action ensures that bit D7 of Interrupt Control Register 1

9

Initialize the rest of the chip as needed

Typical Application

TLF9981 – 19

These components may be necessary to meet UL requirements

for lithium batteries Consult battery manufacturer

14