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XC2200 Derivatives
System Units (Vol. 1 of 2)
System Control Unit (SCU)
User’s Manual
6-206
V2.1, 2008-08
SCU, V1.13
6.10
Temperature Compensation Unit
The temperature compensation for the port drivers provides driver output characteristics
which are stable (within a certain band of parameter variation) over the specified
temperature range.
The temperature compensation oscillator (sensor) provides a reference clock from a
free-running temperature-dependent oscillator. An enable trigger is used to define
counting cycles where the reference clock pulses are accumulated to build the sensor
value TCLR.THCOUNT. The enable trigger is derived from the system clock by a
prescaler and a programmable divider (see
). The value for the
programmable divider must be written by the user according to the selected system
frequency.
After the count cycle, the resulting count value, i.e. the number of reference clock cycles,
is copied to bit field TCLR.THCOUNT. Thus, TCLR.THCOUNT is updated after every
count cycle while the temperature compensation is enabled.
Software can compare the temperature-related count value (TCLR.THCOUNT) to
several thresholds (temperature levels) in order to determine the control values
TCCR.TCC.
Figure 6-30 Temperature Compensation Clock Generation
The clock divider is programmed via bit field TCCR.TCDIV. The value that should be
used for bit field TCCR.TCDIV can be calculated using the following formula
documented in the data sheet.
Generally, temperature compensation is a user-controlled feature. The Temperature
Compensation Control Register TCCR provides access to the actual compensation
value (generated by the sensor) and allows software control of the pads. During
operation the device (i.e. the pads) can be controlled by the value of the on-chip sensor,
or by externally provided compensation values. Register TCCR also provides the
programmable divider value.
Note: The relation between the counter value and the temperature can differ between
two devices and need to be evaluated for each device individually.
32:1
N:1
Prescaler
Programmable Divider
f
Enable
f
SYS
N = (TCDIV+1)
OSC_TC
f
REF