SAF-C164SM Infineon Technologies, SAF-C164SM Datasheet - Page 258

• Manufacturer Part Number: SAF-C164SM
• Description: 16-Bit CMOS Microcontroller
• Manufacturer: Infineon Technologies

Defining the RTC Time Base
The reload timer T14 determines the input frequency of the RTC timer, that is, the RTC
time base, as well as the T14 interrupt cycle time.
range and the T14 reload values (for a time base of 1 s and 1 ms) for several oscillator
frequencies:
Table 14-2
Oscillator
Frequency
32 kHz
4 MHz
5 MHz
8 MHz
10 MHz
12 MHz
16 MHz
Increased RTC Accuracy through Software Correction
The accuracy of the C164CM’s RTC is determined by the oscillator frequency and by the
respective prescaling factor (excluding or including T14). The accuracy limit generated
by the prescaler is due to the quantization of a binary counter (where the average is
zero), while the accuracy limit generated by the oscillator frequency is due to the
difference between the ideal and real frequencies (and therefore accumulates over
time). The total accuracy of the RTC can be further increased via software for specific
applications that demand a high time accuracy.
The key to the improved accuracy is knowledge of the exact oscillator frequency. The
relation of this frequency to the expected ideal frequency is a measure of the RTC’s
deviation. The number of cycles, N, after which this deviation causes an error of 1 cycle
can be easily computed. So, the only action is to correct the count by 1 after each series
of N cycles. This correction may be applied to the RTC register as well as to T14.
Also the correction may be made cyclically, for instance, within T14’s interrupt service
routine, or by evaluating a formula when the RTC registers are read (for this the
respective “last” RTC value must be available somewhere).
Note: For the majority of applications, however, the standard accuracy provided by the
User’s Manual
RTC’s structure will be more than sufficient.
RTC Interrupt Periods and Reload Values
Main 8000 s
Main 64.0 s
Main 51.2 s
Main 32.0 s
Main 25.6 s
Main 21.3 s
Main 16.0 s
Minimum Maximum T14REL Base
RTC Interrupt Period
524.29 s
4.19 s
3.35 s
2.10 s
1.68 s
1.40 s
1.05 s
14-4
FF83
C2F7
B3B5
85EE
676A
48E5
0BDC
Reload Value A
H
H
H
H
H
H
H
Table 14-2
1.000 s
1.000 s
0.999 s
1.000 s
0.999 s
1.000 s
1.000 s
lists the interrupt period
T14REL Base
–
FFF0
FFEC
FFE1
FFD9
FFD2
FFC2
C164CM/C164SM
Reload Value B
Real Time Clock
H
H
H
H
H
H
Derivatives
V1.0, 2002-02
–
1.024 ms
1.024 ms
0.992 ms
0.998 ms
1.003 ms
0.992 ms