ST72C171 datasheet(58/152 Pages) STMICROELECTRONICS

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ST72C171

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16-BIT TIMER (Cont’d)

Notes:

1. After a processor write cycle to the OC

iHR reg-

ister, the output compare function is inhibited

until the OC

iLR register is also written.

2. If the OC

iE bit is not set, the OCMPi pin is a

general I/O port and the OLVL

i bit will not

appear when a match is found but an interrupt

could be generated if the OCIE bit is set.

3. When the timer clock is fCPU/2, OCFi and

OCMP

i are set while the counter value equals

the OC

iR register value (see Figure 8). This

behaviour is the same in OPM or PWM mode.

When the timer clock is fCPU/4, fCPU/8 or in

external clock mode, OCF

i and OCMPi are set

while the counter value equals the OC

iR regis-

ter value plus 1 (see Figure 9).

4. The output compare functions can be used both

for generating external events on the OCMP

pins even if the input capture mode is also

used.

5. The value in the 16-bit OCiR register and the

OLV

i bit should be changed after each suc-

cessful comparison in order to control an output

waveform or establish a new elapsed timeout.

Forced Compare Output capability

When the FOLV

i bit is set by software, the OLVLi

bit is copied to the OCMP

i pin. The OLVi bit has to

be toggled in order to toggle the OCMP

i pin when

it is enabled (OC

iE bit=1). The OCFi bit is then not

set by hardware, and thus no interrupt request is

generated.

FOLVL

i bits have no effect in either One-Pulse

mode or PWM mode.

Figure 36. Output Compare Block Diagram

OUTPUT COMPARE

16-bit

CIRCUIT

OC1R Register

16 BIT FREE RUNNING

COUNTER

OC1E

CC0

CC1

OC2E

OLVL1

OLVL2

OCIE

(Control Register 1) CR1

(Control Register 2) CR2

OCF2

OCF1

(Status Register) SR

16-bit

OCMP1

OCMP2

Latch

OC2R Register

FOLV2 FOLV1

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