Intel 8XC251SA, 8XC251SP Capture Mode, XTAL1 TH2 TL2, TF2, TR2, RCAP2H RCAP2L T2EX EXF2 EXEN2

TIMER/COUNTERS AND WATCHDOG TIMER

Timer 2 provides the following operating modes: capture mode, auto-reload mode, baud rate gen- erator mode, and programmable clock-out mode. Select the operating mode with T2MOD and TCON register bits as shown in Table 8-3 on page 8-15. Auto-reload is the default mode. Setting RCLK and/or TCLK selects the baud rate generator mode.

Timer 2 operation is similar to timer 0 and timer 1. C/T2# selects FOSC /12 (timer operation) or external pin T2 (counter operation) as the timer register input. Setting TF2 allows TL2 to be in- cremented by the selected input.

The operating modes are described in the following paragraphs. Block diagrams in Figures 8-7 through 8-10 show the timer 2 configuration for each mode.

8.6.1Capture Mode

In the capture mode, timer 2 functions as a 16-bit timer or counter (Figure 8-7). An overflow con- dition sets bit TF2, which you can use to request an interrupt. Setting the external enable bit EXEN2 allows the RCAP2H and RCAP2L registers to capture the current value in timer registers TH2 and TL2 in response to a 1-to-0 transition at external input T2EX. The transition at T2EX also sets bit EXF2 in T2CON. The EXF2 bit, like TF2, can generate an interrupt.

XTAL1	12	0	TH2	TL2	Overflow
					TF2
		1	(8 Bits)	(8 Bits)
T2
			TR2
	C/T2#
			Capture		Interrupt
					Request
			RCAP2H RCAP2L
T2EX
					EXF2
			EXEN2
					A4113-02

Figure 8-7. Timer 2: Capture Mode

8-11