STR720 datasheet(321/401 Pages) STMICROELECTRONICS

321 / 401 page

STR720 - EXTENDED FUNCTION TIMER (EFT)

321/401

If OLVLA=1 and OLVLB=0 the length of the pulse is the difference between the OCBR and

OCAR registers.

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

following formula:

Where:

= Desired output compare period (seconds)

fAPB

= APB clock frequency (Hertz)

tPRESC

= Timer clock prescaler ((CC7..CC0)+1)

The Output Compare B event causes the counter to be initialized to FFFCh (See Figure 54).

Note

– The OCFA bit cannot be set by hardware in PWM mode, but OCFB is set every time counter

matches OCBR.

– The Input Capture function is available in PWM mode.

– When Counter = OCBR, then OCFB bit will be set. This can generate an interrupt if OCBIE

is set. This interrupt will help any application where pulse-width or period needs to be

changed interactively.

– When the Pulse Width Modulation (PWM) and One Pulse Mode (OPM) bits are both set with

FOLVA = 0, the PWM mode is the only active one, otherwise the OPM mode is the only ac-

tive one.

– The value loaded in OCBR must always be greater than that in OCAR to produce mean-

ingful waveforms. Note that 0000h is considered to be greater than FFFCh or FFFDh or

FFFEh or FFFFh.

– When OCAR > OCBR, no waveform will be generated.

Figure 53. Pulse Width Modulation Mode Cycle

OCiR Value =

t * fAPB

tPRESC

- 5

Counter

Counter is reset

to FFFCh

OCMPA = OLVLB

Counter

= OCBR

OCMPA = OLVLA

When

= OCAR

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