C8051F120/1/2/3/4/5/6/7
304
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 transition 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 vec-
tors 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
C
F
n
T
O
G
n
P
W
M
n
C
A
P
P
n
C
A
P
N
n
M
A
T
n
PCA0CN
C
F
C
R
C
C
F
0
C
C
F
2
C
C
F
1
C
C
F
5
C
C
F
4
C
C
F
3
Summary of Contents for C8051F120
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Page 8: ...C8051F120 1 2 3 4 5 6 7 8 Rev 1 2 26 2 Flash Programming Commands 318 26 3 Debug Support 321 ...
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