Application Hints

Suggested initialization procedure for DP8571A in battery

1

Enter the test mode by writinga1tobit D7 in the Period-

ic Flag Register

2

Write zero to the RAMTEST mode Register located in

page 0 address HEX 1F

3

Leave the test mode by writinga0tobit D7 in the Peri-

odic Flag Register Steps 1 2 3 guarantee that if the

test mode had been entered during power on (due to

random pulses from the system) all test mode condi-

tions are cleared Most important is that the OSC Fail

Disable bit is cleared Refer to AN-589 for more informa-

tion on test mode operation

4

rect crystal frequency bits (D7 D6 in the Real Time

Mode Register) as shown in Table 1

Table 1

Frequency

D7

D6

32768 KHz

0

0

4194304 MHz

0

1

49152 MHz

1

0

320 KHz

1

1

5

Enter a software loop that does the following

Set a 3 second(approx) software counter The crystal

oscillator may take 1 second to start

51 Writea1tobit D3 in the Real Time Mode Register (try

to start the clock) Make sure the crystal select bits re-

main the same as in step 1 Under normal operation this

bit can be set only if the oscillator is running During the

software loop RAM real time counters output configu-

ration interrupt control and timer functions may be ini-

tialized

6

Test bit D6 in the Periodic Flag Register

IFa1

go to 51 If this bit remains a 1 after 3 seconds

then abort and check hardware The crystal may be

defective or not installed There may be a short at OSC

that is less than 10 MX

IFa0

then the oscillator is running go to step 7

7

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 oscilla-

tor 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

8

Writea1tobit D7 of Interrupt Control Register 1 This

action enables the PFAIL pin and associated circuitry

9

Writea1tobit D4 of the Real Time Mode Register This

action ensures that bit D7 of Interrupt Control Register

10 Initialize the rest of the chip as needed

Typical Application

TLF9979 – 24

These components may be necessary to meet UL requirements for lithium batteries Consult battery manufacturer

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