
C8051F060/1/2/3/4/5/6/7
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Rev. 1.2
25.2.1. Edge-triggered Capture Mode
In this mode, a valid transition on the CEXn pin causes PCA0 to capture the value of the PCA0 counter/
timer and load it into the corresponding module's 16-bit capture/compare register (PCA0CPLn and
PCA0CPHn). The CAPPn and CAPNn bits in the PCA0CPMn register are used to select the type of transi-
tion that triggers the capture: low-to-high transition (positive edge), high-to-low transition (negative edge),
or either transition (positive or negative edge). When a capture occurs, the Capture/Compare Flag (CCFn)
in PCA0CN is set to logic 1 and an interrupt request is generated if CCF interrupts are enabled. The CCFn
bit is not automatically cleared by hardware when the CPU vectors to the interrupt service routine, and
must be cleared by software.
Note: The signal at CEXn must be high or low for at least 2 system clock cycles in order to be valid.
Figure 25.4. PCA Capture Mode Diagram
PCA0L
PCA0CPLn
PCA
Timebase
CEXn
Crossbar
Port I/O
PCA0H
Capture
PCA0CPHn
0
1
0
1
(t
o
CCFn)
PCA Interrupt
PCA0CPMn
P
W
M
1
6
n
E
C
O
M
n
E
C
F
n
T
O
G
n
P
W
M
n
C
A
P
n
C
A
P
N
n
M
A
T
n
PCA0CN
C
F
C
R
C
F
0
C
F
2
C
F
1
C
F
5
C
F
4
C
F
3