ST72344S2 datasheet(104/247 Pages) STMICROELECTRONICS

104 / 247 page

On-chip peripherals

ST72344xx, ST2345xx

104/247

Doc ID 12321 Rev 6

The OC1R register value required for a specific timing application can be calculated using

the following formula:

Where:

●

t = Pulse period (in seconds)

●

fCPU = CPU clock frequency (in Hertz)

●

PRESC

= Timer prescaler factor (2, 4 or 8 depending on the CC[1:0] bits, see Table 50:

Clock control bits)

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

Where:

●

t = Pulse period (in seconds)

●

fEXT = External timer clock frequency (in Hertz)

When the value of the counter is equal to the value of the contents of the OC1R register, the

OLVL1 bit is output on the OCMP1 pin (See Figure 53).

Note:

The OCF1 bit cannot be set by hardware in One-pulse mode but the OCF2 bit can generate

an Output Compare interrupt.

When the Pulse Width Modulation (PWM) and One-pulse mode (OPM) bits are both set, the

PWM mode is the only active one.

If OLVL1=OLVL2 a continuous signal will be seen on the OCMP1 pin.

The ICAP1 pin can not be used to perform input capture. The ICAP2 pin can be used to

perform input capture (ICF2 can be set and IC2R can be loaded) but the user must take

care that the counter is reset each time a valid edge occurs on the ICAP1 pin and ICF1 can

also generates interrupt if ICIE is set.

When One-pulse mode is used, OC1R is dedicated to this mode. Nevertheless, OC2R and

OCF2 can be used to indicate that a period of time has been elapsed but cannot generate

an output waveform, because the OLVL2 level is dedicated to the One-pulse mode.

Figure 53.

One-pulse mode timing example

IEDG1=1, OC1R=2ED0h, OLVL1=0, OLVL2=1.

OCiR Value =

t * fCPU

PRESC

- 5

OCiR =

t * fEXT -5

COUNTER

FFFC FFFD FFFE

2ED0

2ED1 2ED2

2ED3

FFFC FFFD

OLVL2

OLVL1

ICAP1

OCMP1

compare1

01F8

2ED3

IC1R

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