Datasheet

947
SAM4S Series [DATASHEET]
Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14
Figure 39-14. Comparison Unit Block Diagram
The comparison x matches when it is enabled by the bit CEN in the “PWM Comparison x Mode Register”
(PWM_CMPMx for the comparison x) and when the counter of the channel 0 reaches the comparison value
defined by the field CV in “PWM Comparison x Value Register” (PWM_CMPVx for the comparison x). If the
counter of the channel 0 is center aligned (CALG = 1 in “PWM Channel Mode Register” ), the bit CVM (in
PWM_CMPVx) defines if the comparison is made when the counter is counting up or counting down (in left
alignment mode CALG = 0, this bit is useless).
If a fault is active on the channel 0, the comparison is disabled and cannot match (see Section 39.6.2.6 “Fault
Protection”).
The user can define the periodicity of the comparison x by the fields CTR and CPR (in PWM_CMPVx). The
comparison is performed periodically once every CPR+1 periods of the counter of the channel 0, when the value of
the comparison period counter CPRCNT (in PWM_CMPMx) reaches the value defined by CTR. CPR is the
maximum value of the comparison period counter CPRCNT. If CPR=CTR=0, the comparison is performed at each
period of the counter of the channel 0.
The comparison x configuration can be modified while the channel 0 is enabled by using the “PWM Comparison x
Mode Update Register” (PWM_CMPMUPDx registers for the comparison x). In the same way, the comparison x
value can be modified while the channel 0 is enabled by using the “PWM Comparison x Value Update Register”
(PWM_CMPVUPDx registers for the comparison x).
The update of the comparison x configuration and the comparison x value is triggered periodically after the
comparison x update period. It is defined by the field CUPR in the PWM_CMPMx. The comparison unit has an
update period counter independent from the period counter to trigger this update. When the value of the
comparison update period counter CUPRCNT (in PWM_CMPMx) reaches the value defined by CUPR, the update
is triggered. The comparison x update period CUPR itself can be updated while the channel 0 is enabled by using
the PWM_CMPMUPDx register.
CAUTION:
to be taken into account, the write of the register PWM_CMPVUPDx must be followed by a write of the
register PWM_CMPMUPDx.
The comparison match and the comparison update can be source of an interrupt, but only if it is enabled and not
masked. These interrupts can be enabled by the “PWM Interrupt Enable Register 2” and disabled by the “PWM
Interrupt Disable Register 2” . The comparison match interrupt and the comparison update interrupt are reset by
reading the “PWM Interrupt Status Register 2” .
=
fault on channel 0
CNT [PWM_CCNT0]
CNT [PWM_CCNT0] is decrementing
CALG [PWM_CMR0]
CV [PWM_CMPVx]
=
1
0
1
Comparison x
CVM [PWM_CMPVx]
=
CPRCNT [PWM_CMPMx]
CTR [PWM_CMPMx]
CEN [PWM_CMPM]x