XC886/888CLM
Capture/Compare Unit 6
User’s Manual
14-3
V1.3, 2010-02
CCU6, V 1.0
14.1
Functional Description
14.1.1
Timer T12
The timer T12 is built with three channels in capture/compare mode. The input clock for
timer T12 can be from
f
CCU6
to a maximum of
f
CCU6
/128 and is configured by bit field
T12CLK. In order to support higher clock frequencies, an additional prescaler factor of
1/256 can be enabled for the prescaler of T12 if bit T12PRE = 1.
The timer period, compare values, passive state selects bits and passive levels bits are
written to shadow registers and not directly to the actual registers, while the read access
targets the registers actually used (except for the three compare channels, where both
the actual and the shadow registers can be read). For example, a read access to T12PR
delivers the current period value at the comparator, whereas a write access targets the
internal Shadow Period Register T12PS to prepare another period value. The transfer
from the shadow registers to the actual registers is enabled by setting the shadow
transfer enable bit STE12.
If this transfer is enabled, the shadow registers are copied to the respective registers as
soon as the associated timer reaches the value zero the next time (being cleared in
edge-aligned mode or counting down to 1 in center-aligned mode). When timer T12 is
operating in center-aligned mode, it will also copy the registers (if enabled by STE12) if
it reaches the currently programmed period value (counting up).
When timer T12 is stopped, the shadow transfer takes place immediately if the
corresponding bit STE12 is set. Once the transfer is complete, the respective bit STE12
is cleared automatically.
shows an overview of Timer T12.
Figure 14-2
T12 Overview
CC6xR
CC6xSR
= ?
counter
register T12
compare-match
= 0 ?
= 1 ?
zero-match
one-match
T12PR
T12PS
= ?
period shadow transfer
period-match
capture events
according to
bitfield MSEL6x
T12clk
compare shadow transfer
16
16
16
CCU6_T12_overv
*
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