SM8580 datasheet(22/23 Pages) NPC

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SM8580AM

NIPPON PRECISION CIRCUITS—22

APPLICATION NOTES

Setting the Alarm

Alarms can be set for day, weekday, hour, minute,

and second. However, it is not possible to set an

alarm for more than one weekday.

Note that it is recommended that AF and AIE be set

to 0 at the same time to avoid accidental hardware

interrupts while setting the alarm. After the alarm

data is entered, initialization occurs when AF is

again set to 0.

If the interrupt output is not used by setting AIE set

to 0, an alarm can still be controlled by software

monitoring of the AF bit.

Example 1

To set an alarm for 6pm of the following day:

• Set bits AIE and AF to 0.

• Set the day register AE bit to 1.

• Acquire the current weekday setting from bank

0 register 6, add 1 to the current value (except in

the case of Saturday), and write the updated

data. Note that the day following 6H (Saturday)

is 0H (Sunday).

• Write 18H to the hour alarm register.

• Write 00H to the minute alarm register.

• Write 00H to the seconds alarm register.

• Set bit AF to 0.

• Set bit AIE to 1.

Example 2

To set an alarm for 6am on every for Sunday:

• Set bits AIE and AF to 0.

• Set the day alarm register AE bit to 1.

• Write 0H to the weekday alarm register.

• Write 06H to the hour alarm register.

• Write 00H to the minute alarm register.

• Write 00H to the seconds alarm register.

• Set bit AF to 0.

• Set bit AIE to 1.

Using the Temperature Sensor

The SM8580AM temperature sensor can be used to

monitor the surrounding temperature. The tempera-

ture sensor information can then be used to adjust the

clock for any temperature variations in the oscillator

frequency which affect the accuracy of the clock.

One method of utilizing the temperature sensor to

adjust timing errors is by using the clock error cor-

rection function (digital correction), as described

below.

1. Based on the known temperature characteristics

of the oscillator crystal, store temperature cor-

rection values for various temperatures in an

external non-volatile EEPROM.

2. Use an A/D converter, such as in a general-pur-

pose CPU, to convert the VTEMP temperature

sensor output voltage into a digital value.

3. Use the digital value of the current temperature

to access the temperature correction data stored

in the EEPROM, and then write the correspond-

ing data into the digital correction registers.

This procedure is useful in implementing a high-

accuracy clock function.

Monitoring Digital Correction

Using the test mode allows the 64Hz digital correc-

tion clock to be output on pin FOUT. The test mode

works as follows.

1. Apply a HIGH-level on FCON.

2. Set the FOUT frequency set register FE bit to 1.

3. Set the CE1 control register CDT_ON bit to 1.

4. Set correction data in the digital correction regis-

ter DT0 to DT6 bits, and then set DT_ON to 1.

5. Set the bank 2 register C, bit 1 to 1.

6. When CE0N is LOW and CE1 is HIGH and the

test mode set register TEST bit is set to 1, the

digital correction cycle changes from 10 seconds

to 1/64 seconds, and the clock output on FOUT

is the 64Hz clock after timing correction. The

output is the corrected timing for the set digital

correction value corresponding to a 64Hz clock

× 64[ppm]. Measuring this output provides a

quick method for monitoring the digital correc-

tion function.

7. When CE0N goes HIGH, the TEST bit is reset to

1 and test mode is released.

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