Silicon Laboratories C8051F342, C8051F347 Programmable Counter Array PCA0, PCA Block Diagram

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

22. Programmable Counter Array (PCA0)

The Programmable Counter Array (PCA0) provides enhanced timer functionality while requiring less CPU intervention than the standard 8051 counter/timers. The PCA consists of a dedicated 16-bit counter/timer and five 16-bit capture/compare modules. Each capture/compare module has its own associated I/O line (CEXn) which is routed through the Crossbar to Port I/O when enabled (See Section “15.1. Priority Crossbar Decoder” on page 149 for details on configuring the Crossbar). The counter/timer is driven by a programmable timebase that can select between six sources: system clock, system clock divided by four, system clock divided by twelve, the external oscillator clock source divided by 8, Timer 0 overflow, or an external clock signal on the ECI input pin. Each capture/compare module may be configured to operate independently in one of six modes: Edge-Triggered Capture, Software Timer, High-Speed Output, Fre- quency Output, 8-Bit PWM, or 16-Bit PWM (each mode is described in Section “22.2. Capture/Compare Modules” on page 265). The external oscillator clock option is ideal for real-time clock (RTC) functionality, allowing the PCA to be clocked by a precision external oscillator while the internal oscillator drives the sys- tem clock. The PCA is configured and controlled through the system controller's Special Function Regis- ters. The PCA block diagram is shown in Figure 22.1

Important Note: The PCA Module 4 may be used as a watchdog timer (WDT), and is enabled in this mode following a system reset. Access to certain PCA registers is restricted while WDT mode is enabled. See Section 22.3 for details.

	SYSCLK/12
	SYSCLK/4
	Timer 0 Overflow		PCA	16-Bit Counter/Timer
	ECI		CLOCK
	SYSCLK		MUX
	External Clock/8
	Capture/Compare	Capture/Compare		Capture/Compare	Capture/Compare	Capture/Compare
	Module 0		Module 1	Module 2	Module 3	Module 4 / WDT
ECI	CEX0		CEX1	CEX2	CEX3	CEX4
			Crossbar

Port I/O

Figure 22.1. PCA Block Diagram

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