YMF754-R datasheet(47/60 Pages) YAMAHA

47 / 60 page

YMF754

June 28, 1999

-47-

5. Hardware Volume Control

The hardware volume control determines the AC’97 master volume without using any software control using

the external circuit listed below.

Two pins, VOLUP# for increasing the volume and VOLDW# for decreasing the volume, are used.

VOLDW#

VOLUP#

1000p

Push SW

DS-1E provides a shadow register for the AC’97 master volume.

When the software accesses the AC’97

master volume, it is always reflected in the shadow register.

Bringing the VOLUP# pin LOW level increments the left and right-channel shadow register by +1.5dB

respectively.

If either one of channel shadow registers have been already set to maximum value (00000b),

the corresponding channel shadow register remains in the same value, and the other channel shadow register

will only be incremented.

If both of channel shadow registers have been already set to maximum values,

they remain in the same values.

Bringing the VOLDW# pin LOW level decrements the left and right-channel shadow register by -1.5dB

respectively.

If either one of channel shadow registers have been already set to minimum value (11111b),

the corresponding channel shadow register remains in the same value, and the other channel shadow register

will only be decremented.

If both of channel shadow registers have been already set to minimum values,

they remain in the same values.

The master volume for the AC’97 is updated automatically via the AC-Link by setting corresponding values

to the shadow registers.

When both of the VOLUP# and VOLDW# pins are at LOW level at the same time, the MUTE bit of the

shadow register is enabled to automatically set the MUTE bit of the AC’97 master volume via the AC-Link.

When either one of the VOLUP# or VOLDW# pins is at LOW level, mute condition of the AC’97 is

deactivated via the AC-Link.

At this point of time, the master volume is set to the value before the mute.

When the AC-Link is busy (in case the register is controlled by the AC’97 Control Register), shadow register

values will be set to the AC’97 on the next frame.

At this time, BUSY is set at the AC’97 control register.

When the master volume is changed or muted depending on the logic level transition status of the VOLUP#

and VOLDW# pins, an interrupt is generated at the host.

The interrupt is used to notify the driver that the

master volume has been changed.

When the AC’97 is not connected or it is placed in power down mode, the shadow register values will remain

in the same even if the VOLDW# and VOLUP# pins are at LOW level.

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