ACE5372

Low Power Real-Time Clock (RTC)

VER 1.3

22

Example of Calculations

1) When oscillation frequency = 32770kHz; target frequency = 32768kHz

Adjustment value = （32770-32768+0.1）/(32770*2/(32768*20))

=(32770-32768)*10+1=21

Set （F6，F5，F4，F3，F2，F1，F0）=（0，0，1，0，1，0，1）

2) When oscillation frequency =32762kHz; target frequency = 32768kHz

Adjustment value =（32762-32768）/(32762*2/(32768*20))

= (32762-32768)*10=-60

To express

–60 in 7bi binary digits with sign bit ( two’s compliment)

Subtract 60(3Ch) from 128(80h) in the above case, 80h-3Ch=44h

Thus set （F6，F5，F4，F3，F2，F1，F0）=（1，0，0，0，1，0，0）

After adjustment, adjustment error against the target frequency will the approx. ±1.5ppm at a room

temperature.

Notice:

1) Clock frequency output from the

INTRB pin will change after adjustment by the clock adjustment circuit.

2) Adjustment range:

A)When oscillation frequency is higher than target frequency, the range of adjustment values is （F6，F5，F4，F3，F2，F1，

F0）=（0，0，0，0，0，0，1）to (0，1，1，1，1，1，1) and actual adjustable amount shall be -3.05ppm to

–189.2ppm (-3.125ppm

to 193.7ppm for 32000Hz crystal).

B) When oscillation frequency is lower than target frequency, the range of adjustment values is （F6，F5，F4，F3，F2，F1，

F0）=（1，1，1，1，1，1，1）to（1，0，0，0，0，1，0）and actual adjustable amount shall be 3.05ppm to 189.2ppm (3.125ppm

to 193.7ppm for 32000Hz crystal)

Output Waveforms

The following three output waveforms can be output from the

INTRA (INTRB) pin.

1）Alarm interrupt

When a registered time for alarm (such as day-of-the-week, hour or minute) coincide with calendar

counter (such as day-of-the-week, hour or minute) interrupt to the CPU are requested with the output pin

being on “L”. Alarm interrupt consists of Alarm_A and Alarm_B, both have equivalent functions.

2）Periodic interrupt

Outputs an output waveform selected by setting the periodic interrupt frequency select bit. Waveforms

include pulse mode and level mode.

3）32KHz clock output

Clock pulses generated in the oscillation circuit are output as they are.