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C167CS
Derivatives
The Capture/Compare Units
16.4
Capture Mode
In response to an external event the content of the associated timer (T0/T1 or T7/T8,
depending on the used CAPCOM unit and the state of the allocation control bit ACCx) is
latched into the respective capture register CCx. The external event causing a capture
can be programmed to be either a positive, a negative, or both a positive or a negative
transition at the respective external input pin CCxIO.
The triggering transition is selected by the mode bits CCMODx in the respective
CAPCOM mode control register. In any case, the event causing a capture will also set
the respective interrupt request flag CCxIR, which can cause an interrupt or a PEC
service request, when enabled.
Edge
Select
Capture Reg. CCx
Interrupt
Request
CCxIO
CCMODx
Input
Clock
CAPCOM Timer Ty
x = 31...0
y = 0, 1, 7, 8
Interrupt
Request
MCB02015
Figure 16-5 Capture Mode Block Diagram
In order to use the respective port pin as external capture input pin CCxIO for capture
register CCx, this port pin must be configured as input, i.e. the corresponding direction
control bit must be set to ‘0’. To ensure that a signal transition is properly recognized, an
external capture input signal should be held for at least 8 CPU clock cycles before it
changes its level.
During these 8 CPU clock cycles the capture input signals are scanned sequentially.
When a timer is modified or incremented during this process, the new timer contents will
already be captured for the remaining capture registers within the current scanning
sequence.
Note: When the timer modification can generate an overflow the capture interrupt
routine should check if the timer overflow was serviced during these 8 CPU clock
cycles.
If pin CCxIO is configured as output, the capture function may be triggered by modifying
the corresponding port output latch via software, e.g. for testing purposes.
User’s Manual
16-13
V2.0, 2000-07