ST72324BJ2 datasheet(76/188 Pages) STMICROELECTRONICS

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On-chip peripherals

ST72324B

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Output compare

In this section, the index, i, may be 1 or 2 because there are two output compare functions in

the 16-bit timer.

This function can be used to control an output waveform or indicate when a period of time

has elapsed.

When a match is found between the Output Compare register and the free running counter,

the output compare function:

–

Assigns pins with a programmable value if the OCiE bit is set

–

Sets a flag in the status register

–

Generates an interrupt if enabled

Two 16-bit registers Output Compare register 1 (OC1R) and Output Compare register 2

(OC2R) contain the value to be compared to the counter register each timer clock cycle.

These registers are readable and witable and are not affected by the timer hardware. A

reset event changes the OCiR value to 8000h.

Timing resolution is one count of the free running counter: (fCPU/CC[1:0]).

Procedure

To use the Output Compare function, select the following in the CR2 register:

●

Set the OCiE bit if an output is needed then the OCMPi pin is dedicated to the output

compare i signal.

●

Select the timer clock (CC[1:0]) (see Table 49).

And select the following in the CR1 register:

●

Select the OLVLi bit to applied to the OCMPi pins after the match occurs.

●

Set the OCIE bit to generate an interrupt if it is needed.

When a match is found between OCRi register and CR register:

●

OCFi bit is set

●

The OCMPi pin takes OLVLi bit value (OCMPi pin latch is forced low during reset)

●

A timer interrupt is generated if the OCIE bit is set in the CR1 register and the I bit is

cleared in the CC register (CC).

The OCiR register value required for a specific timing application can be calculated using

the following formula:

Where:

∆t

= Output compare period (in seconds)

fCPU

= CPU clock frequency (in hertz)

PRESC = Timer prescaler factor (2, 4 or 8 depending on CC[1:0] bits; see Table 49)

Table 44.

Output compare byte distribution

MS byte

LS byte

OCiR

OCiHR

OCiLR

∆ OCiR =

∆t * fCPU

PRESC

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