SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 118

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

On-Chip Peripheral Components
Figure 7-50
Modulation Range of a PWM Signal Generated with a Compare Timer/CMx Register
Combination
Thus "TOC-Ioading" means that there is dedicated hardware in the CCU which synchronizes the
loading of the compare registers CMx in such a way that there is no loss of compare events. lt also
relieves the CPU of interrupt load.
What does this hardware look like:
A CMx compare register in compare mode 0 consists of two latches. When the CPU tries to access
a CMx register it only addresses a register latch and not the actual compare latch which is
connected to the comparator circuit. The contents of the register latch may be changed by the CPU
at any time because this change would never affect the compare event for the current timer period.
The compare latch (the "actual" latch) holds the compare value for the present timer period. Thus
the CPU only changes the compare event for the next timer period since the loading of the latch is
performed by the timer overflow signal of the compare timer.
This means for an application which uses several PWM outputs that the CPU does not have to
serve every single compare line by an individual interrupt. lt only has to watch the timer overflow of
the compare timer and may then set up the compare events of all compares for the next timer
period. This job may take the whole current timer period since the TOC loading prevents
unintentional overwriting of the actual (and prepared) value in the compare latch.
Semiconductor Group
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