SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 102

• Manufacturer Part Number: SAB80C517-M16
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

When the reload register is to be loaded with a 16-bit value, the high byte of CTREL must be written
first to ensure a determined start or restart position. Writing to the low byte then triggers the actual
reload procedure mentioned above. The 16-bit reload value can be overwritten at any time.
Overflow Interrupt of the Compare Timer
The compare timer has - as any other timer in the SAB 80C517 - its own interrupt request flag, which
is in this case called CTF. This flag is located in register CTCON.CTF and is set when the timer
count rolls over from all ones to the reload value.
The overflow interrupt eases e.g. software control of pulse width modulated output signals. A
periodic interrupt service routine caused by an overflow of the compare timer can be used to load
new values in the assigned compare registers and thus change the corresponding PWM output
accordingly.
Please refer to section 8 for details about the overflow interrupt (enabling, vector address, priority,
etc.).
7.5.3
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 SAB 80C517, two
compare modes are implemented to cover a wide range of possible applications (see section 7.5.4
below).
- 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.
7.5.4
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
In the SAB 80C517 - thanks to the high number of 13 compare registers and two associated timers
Compare Function in the CCU
Compare Modes of the CCU
103
On-Chip Peripheral Components