ST72344K2 datasheet(100/247 Pages) STMICROELECTRONICS

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On-chip peripherals

ST72344xx, ST2345xx

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Doc ID 12321 Rev 6

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 writable and are not affected by the timer hardware. A

reset event changes the OCiR value to 8000h.

The 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 50: Clock control bits).

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 CR2 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:

●

Δt = 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 50)

If the timer clock is an external clock, the formula is:

Where:

●

Δt = Output compare period (in seconds)

●

fEXT = External timer clock frequency (in Hertz)

Table 46.

OCiR register

MS Byte

LS Byte

OCiROCiHR

OCiLR

Δ OCiR = Δ

t * fCPU

PRESC

Δ OCiR = Δt

* fEXT

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