Intel 8XC251SP, 8XC251SA Auto-reload Mode, Up Counter Operation, RCAP2H RCAP2L TF2, EXF2 EXEN2

8XC251SA, SB, SP, SQ USER’S MANUAL

8.6.2Auto-reload Mode

The auto-reload mode configures timer 2 as a 16-bit timer or event counter with automatic reload. The timer operates an as an up counter or as an up/down counter, as determined by the down counter enable bit (DCEN). At device reset, DCEN is cleared, so in the auto-reload mode, timer 2 defaults to operation as an up counter.

8.6.2.1Up Counter Operation

When DCEN = 0, timer 2 operates as an up counter (Figure 8-8). The external enable bit EXEN2 in the T2CON register provides two options (Figure 8-12). If EXEN2 = 0, timer 2 counts up to FFFFH and sets the TF2 overflow flag. The overflow condition loads the 16-bit value in the re- load/capture registers (RCAP2H, RCAP2L) into the timer registers (TH2, TL2). The values in RCAP2H and RCAP2L are preset by software.

If EXEN2 = 1, the timer registers are reloaded by either a timer overflow or a high-to-low tran- sition at external input T2EX. This transition also sets the EXF2 bit in the T2CON register. Either TF2 or EXF2 bit can generate a timer 2 interrupt request.

XTAL1	12	0	TH2	TL2	Overflow
		1	(8 Bits)	(8 Bits)
T2			TR2
	C/T2#		Reload
			RCAP2H RCAP2L
				TF2	Interrupt
T2EX					Request
				EXF2
		EXEN2
					A4115-02

Figure 8-8. Timer 2: Auto Reload Mode (DCEN = 0)

8-12