Specifications

C8051F330/1
188 Rev. 1.1
19.2.1. Edge-triggered Capture Mode
In this mode, a valid transition on the CEXn pin causes the PCA to capture the value of the PCA 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. If both CAPPn and CAPNn bits are set to
logic
1, then the state of the Port pin associated with CEXn can be read directly to determine whether a rising-edge or
falling-edge caused the capture.
Note: The CEXn input signal must remain high or low for at least 2 system clock cycles to be recognized by the hard-
ware.
Figure 19.4. PCA Capture Mode Diagram
PCA0L
PCA0CPLn
PCA
Timebase
CEXn
CrossbarPort I/O
PCA0H
Capture
PCA0CPHn
0
1
0
1
(to CCFn)
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
4
C
C
F
3
PCA Interrupt
0x00xx