C8051F340/1/2/3/4/5/6/7

22.2.1. 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

PCA Interrupt

Port I/O Crossbar

CEXn

PE C C M T P E W C A A A O W C M O P P T G M C 1 M P N n n n F

6

n n n

 

n

n

 

 

 

 

 

x 0

 

 

0 0 0 x

 

 

 

 

 

 

 

 

 

 

 

 

0

1

0

1

PCA0CN

C C C C C C C F R C C C C C F F F F F 4 3 2 1 0

CCFn)(to

PCA0CPLn PCA0CPHn

Capture

PCA

PCA0L

PCA0H

Timebase

 

 

Figure 22.4. 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.

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Silicon Laboratories C8051F341, C8051F347, C8051F346, C8051F343 PCA Capture Mode Diagram, Edge-triggered Capture Mode