Intel 8XC251SA, 8XC251SP, 8XC251SQ, 8XC251SB, Embedded Microcontroller manual PCA 16-bit Capture Mode

8XC251SA, SB, SP, SQ USER’S MANUAL

To program a compare/capture module for the 16-bit capture mode, program the CAPPx and CAPNx bits in the module’s CCAPM x register as follows:

•To trigger the capture on a positive transition, set CAPPx and clear CAPNx.

•To trigger the capture on a negative transition, set CAPNx and clear CAPPx.

•To trigger the capture on a positive or negative transition, set both CAPPx and CAPNx.

Table 9-3 on page 9-14 lists the bit combinations for selecting module modes. For modules in the capture mode, detection of a valid signal transition at the I/O pin (CEXx) causes hardware to load the current PCA timer/counter value into the compare/capture registers (CCAPxH/CCAPxL) and to set the module’s compare/capture flag (CCFx) in the CCON register. If the corresponding in- terrupt enable bit (ECCFx) in the CCAPMx register is set (Figure 9-9), the PCA sends an interrupt request to the interrupt handler.

Since hardware does not clear the event flag when the interrupt is processed, the user must clear the flag in software. A subsequent capture by the same module overwrites the existing captured value. To preserve a captured value, save it in RAM with the interrupt service routine before the next capture event occurs.

						PCA Timer/Counter
				Count		CH	CL
				Input		(8 Bits)	(8 Bits)
CEXx				Capture
External I/O
						CCAPxH CCAPxL
x = 0,1,2,3 or 4						Interrupt
X = Don't Care
						Request
			CCFx
			CCON Register			Enable
X	O	CAPPx CAPNx	O	O	O	ECCFx
7		CCAPMx Mode Register				0
							A4163-02

Figure 9-2. PCA 16-bit Capture Mode

9-6