AT90PWM2 datasheet(139/361 Pages) ATMEL

139 / 361 page

139

4317J–AVR–08/10

AT90PWM2/3/2B/3B

16.5.3

Fifty Percent Waveform Configuration

When PSCOUTn0 and PSCOUTn1 have the same characteristics, it’s possible to configure the

PSC in a Fifty Percent mode. When the PSC is in this configuration, it duplicates the OCRn-

SBH/L and OCRnRBH/L registers in OCRnSAH/L and OCRnRAH/L registers. So it is not

necessary to program OCRnSAH/L and OCRnRAH/L registers.

16.6

Update of Values

To avoid unasynchronous and incoherent values in a cycle, if an update of one of several values

is necessary, all values are updated at the same time at the end of the cycle by the PSC. The

new set of values is calculated by sofware and the update is initiated by software.

Figure 16-11. Update at the end of complete PSC cycle.

The software can stop the cycle before the end to update the values and restart a new PSC

cycle.

16.6.1

Value Update Synchronization

New timing values or PSC output configuration can be written during the PSC cycle. Thanks to

LOCK and AUTOLOCK configuration bits, the new whole set of values can be taken into

account after the end of the PSC cycle.

When AUTOLOCK configuration is selected, the update of the PSC internal registers will be

done at the end of the PSC cycle if the Output Compare Register RB has been the last written.

The AUTOLOCK configuration bit is taken into account at the end of the first PSC cycle.

When LOCK configuration bit is set, there is no update. The update of the PSC internal registers

will be done at the end of the PSC cycle if the LOCK bit is released to zero.

The registers which update is synchronized thanks to LOCK and AUTOLOCK are PSOCn,

POM2, OCRnSAH/L, OCRnRAH/L, OCRnSBH/L and OCRnRBH/L.

See these register’s description starting on page 162.

When set, AUTOLOCK configuration bit prevails over LOCK configuration bit.

See “PSC 0 Configuration Register – PCNF0” on page 163.

16.7

Enhanced Resolution

Lamp Ballast applications need an enhanced resolution down to 50Hz. The method to improve

the normal resolution is based on Flank Width Modulation (also called Fractional Divider).

Cycles are grouped into frames of 16 cycles. Cycles are modulated by a sequence given by the

Software

PSC

Regulation Loop

Calculation

Writting in

PSC Registers

Cycle

With Set i

Cycle

With Set i

Cycle

With Set i

Cycle

With Set i

Cycle

With Set j

End of Cycle

Request for

an Update

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