Intel 8XC251SP, 8XC251SA, 8XC251SQ, 8XC251SB manual Compare Modes, 3 16-bit Software Timer Mode

PROGRAMMABLE COUNTER ARRAY

9.3.2Compare Modes

The compare function provides the capability for operating the five modules as timers, event counters, or pulse width modulators. Four modes employ the compare function: 16-bit software timer mode, high-speed output mode, WDT mode, and PWM mode. In the first three of these, the compare/capture module continuously compares the 16-bit PCA timer/counter value with the 16- bit value pre-loaded into the module’s CCAPxH/CCAPxL register pair. In the PWM mode, the module continuously compares the value in the low-byte PCA timer/counter register (CL) with an 8-bit value in the CCAPxL module register. Comparisons are made three times per peripheral cycle to match the fastest PCA timer/counter clocking rate (FOSC/4). For a description of periph- eral cycle timing, see section 2.2.2, “Clock and Reset Unit.”

Setting the ECOMx bit in a module’s mode register (CCAPMx) selects the compare function for that module (Figure 9-9 on page 9-15). To use the modules in the compare modes, observe the following general procedure:

1.Select the module’s mode of operation.

2.Select the input signal for the PCA timer/counter.

3.Load the comparison value into the module’s compare/capture register pair.

4.Set the PCA timer/counter run control bit.

5.After a match causes an interrupt, clear the module’s compare/capture flag.

9.3.316-bit Software Timer Mode

To program a compare/capture module for the 16-bit software timer mode (Figure 9-3), set the ECOMx and MATx bits in the module’s CCAPM x register. Table 9-3 lists the bit combinations for selecting module modes.

Amatch between the PCA timer/counter and the compare/capture registers (CCAPxH/CCAPxL) sets the module’s compare/capture flag (CCFx in the CCON register). This generates an interrupt request if the corresponding interrupt enable bit (ECCFx in the CCAPMx register) is set. Since hardware does not clear the compare/capture flag when the interrupt is processed, the user must clear the flag in software. During the interrupt routine, a new 16-bit compare value can be written to the compare/capture registers (CCAPxH/CCAPxL).

NOTE

To prevent an invalid match while updating these registers, user software should write to CCAPxL first, then CCAPxH. A write to CCAPxL clears the ECOMx bit disabling the compare function, while a write to CCAPxH sets the ECOMx bit re-enabling the compare function.

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