ST7LITE49K2 datasheet(118/245 Pages) STMICROELECTRONICS

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On-chip peripherals

ST7LITE49K2

118/245

16-bit read sequence (from either the counter register or the alternate counter register)

Figure 56.

16-bit read sequence

The user must read the MSB first, then the LSB value is buffered automatically.

This buffered value remains unchanged until the 16-bit read sequence is completed, even if

the user reads the MSB several times.

After a complete reading sequence, if only the CLR register or ACLR register are read, they

return the LSB of the count value at the time of the read.

Whatever the timer mode used (input capture, output compare, one pulse mode or PWM

mode) an overflow occurs when the counter rolls over from FFFFh to 0000h then:

●

The TOF bit of the SR register is set.

●

A timer interrupt is generated if:

–

TOIE bit of the CR1 register is set and

–

I bit of the CC register is cleared.

If one of these conditions is false, the interrupt remains pending to be issued as soon as

they are both true.

Clearing the overflow interrupt request is done in two steps:

Reading the SR register while the TOF bit is set.

An access (read or write) to the CLR register.

Note:

The TOF bit is not cleared by accesses to ACLR register. The advantage of accessing the

ACLR register rather than the CLR register is that it allows simultaneous use of the overflow

function and reading the free running counter at random times (for example, to measure

elapsed time) without the risk of clearing the TOF bit erroneously.

The timer is not affected by Wait mode.

In Halt mode, the counter stops counting until the mode is exited. Counting then resumes

from the previous count (device awakened by an interrupt) or from the reset count (device

awakened by a reset).

External clock

The external clock (where available) is selected if CC0 = 1 and CC1 = 1 in CR2 register.

The status of the EXEDG bit in the CR2 register determines the type of level transition on

the external clock pin EXTCLK that triggers the free running counter.

The counter is synchronized with the falling edge of the internal CPU clock.

Read MSB

At t0

Returns the buffered

LSB value at t0

At t0 +

Δt

Other

instructions

Beginning of the sequence

Sequence completed

LSB is buffered

Read LSB

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