C509-L_97 Datasheet, PDF (122/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C509-L
6.3.3 Compare Functions of the CCU
The compare function of a timer/register combination can be described as follows. The 16-bit value
stored in a compare or compare/capture register is compared with the contents of the timer register.
lf the count value in the timer register matches the stored value, an appropriate output signal is
generated at a corresponding port pin.
The contents of a compare register can be regarded as ’time stamp’ at which a dedicated output
reacts in a predefined way (either with a positive or negative transition). Variation of this ’time stamp’
somehow changes the wave of a rectangular output signal at a port pin. This may - as a variation
of the duty cycle of a periodic signal - be used for pulse width modulation as well as for a continually
controlled generation of any kind of square wave forms. In the case of the C509-L, two compare
modes are implemented to cover a wide range of possible applications.
In the C509-L - thanks to the high number of 21 compare registers and two associated timers -
several timer/compare register combinations are selectable. In some of these configurations one of
the two compare modes may be freely selected, others, however, automatically establish a
compare mode. In the following the two possible modes are generally discussed. This description
will be referred to in later sections where the compare registers are described.
As already mentioned, there are only a few compare registers with their corresponding port circuitry
which are able to serve both compare modes. In most cases the mode is automatically set
depending on the timer which is used as time base or depending on the port which outputs the
compare signal.
Semiconductor Group
6-44
1997-10-01