C8051F52X Datasheet, PDF (202/220 Pages) Silicon Laboratories – 8/4/2 kB ISP Flash MCU Family

C8051F52x-53x
20.2.1. 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 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. 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.
PCA0CPMn
P ECCMT P E
WCA A AOWC
MOPP TGMC
1 MPN n n n F
6nnn
n
n
PCA Interrupt
PCA0CN
CC
CCC
FR
CCC
FFF
210
Port I/O
Crossbar ^CEXn
0
1
0
1
PCA0CPLn PCA0CPHn
Capture
PCA
Timebase
PCA0L
PCA0H
Figure 20.4. PCA Capture Mode Diagram
Note: The CEXn input signal must remain high or low for at least 2 system clock cycles to be recognized
by the hardware.
202
Rev. 0.3