aduc7032 Analog Devices, Inc., aduc7032 Datasheet - Page 72

• Manufacturer Part Number: aduc7032
• Description: Microconverter Integrated, Precision Battery Sensor
• Manufacturer: Analog Devices, Inc.

Preliminary Technical Data
ADUC7032 LOW POWER CLOCK CALIBRATION
The low power 131kHz oscillator may be calibrated using either
the precision 131kHz oscillator, or an external 32.768KHz
watch crystal. Two dedicated calibration counters and an
oscillator trim register are used to implement this feature.
One counter, 9-bits wide, is clocked by the accurate clock
oscillator, either the Precision oscillator or external watch
crystal. The second counter, 10-bits wide, is clocked by the low
power oscillator, either directly at 131kHz or via a divide by 4
block generating 32.768kHz. The source for each calibration
counter should be of the same frequency. The trim register
(OSC0TRM) is an 8-bit wide register, the lower 4-bits of which
are user accessible trim bits. Increasing the value in OSC0TRM
will decrease the frequency of the low power oscillator,
decreasing the value will increase the frequency. Based on a
nominal frequency of 131KHz, the typical trim range is
between 127KHz to 135KHz. The OSC0TRIM bits have a
resolution of typically 500Hz per LSB.
The clock calibration mode is configured and controlled by the
following MMRs:
An example calibration routine is shown in Figure 28. User
code configures and enables the calibration sequence via
OSC0CON. When the precision oscillator calibration counter,
OSC0VAL0, reaches 0x1FF, both counters are disabled.
User code then reads back the value of the low power oscillator
calibration counter. There are three possible scenarios:
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-
-
-
-
-
-
-
OSC0CON:
OSC0STA:
OSC0VAL0:
OSC0VAL1:
OSC0TRM:
OSC0VAL0 < OSC0VAL1. The Low Power Oscillator
OSC0VAL0 = OSC0VAL1. No Further Action is
required.
OSC0VAL0 > OSC0VAL1. The Low Power Oscillator
is running slow. OSC0TRM must be decreased.
is running fast. OSC0TRM must be increased.
Control bits for calibration,
Calibration Status Register
9Bit counter. Counter 0
10Bit counter. Counter 1
Oscillator Trim Register
Rev. PrD | Page 72 of 128
When the OSC0TRM has been changed the routine should be
re-run and the new frequency checked.
Using the internal precision 131kHz oscillator, it will take
approximately 4milliseconds to execute the calibration routine.
If the external 32.768kHz crystal is used, this time increases to
16milliseconds.
NOTE: Prior to the clock calibration routine been started, it is
required that the user switch to either the precision 131kHz
oscillator or the external 32.768KHz watch crystal as the PLL
Clock Source. If this is note done, it is possible that the PLL will
lose lock each time OSC0TRM is modified. This will increase
the length of time it takes to calibrate the Low Power,
Oscillator.
OSC0VAL0 < OSC0VAL1
INCREASE
OSC0TRM
Figure 28 : Example OSC0TRM Calibration Routine
NO
OSC0VAL0 = OSC0VAL1
IS ERROR WITHIN
DESIRED LEVEL?
OSCSTA[0] = 1
CALIBRATION
CALIBRATION
ROUTINE
ROUTINE
BEGIN
WHILE
END
YES
OSC0VAL0 > OSC0VAL1
DECREASE
OSC0TRM
ADuC7032