YMF724F datasheet(41/50 Pages) YAMAHA

41 / 50 page

YMF724F

January 14, 1999

-41-

6. 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-1 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.

The value of the shadow register is incremented by 1.5dB on the rising edge of the signal input to the

VOLUP# pin.

If it is already set to the maximum value, it does not change.

The value set in the shadow

The value of the shadow register is decremented by 1.5dB on the rising edge of the signal input to the

VOLDW# pin.

If it is already set to the minimum value, it does not change.

The value set in the shadow

Also, when both VOLUP#, VOLDW# pins are at LOW level, the MUTE bit of the shadow address is enabled

and the Master Volume Mute bit of the AC’97 register is automatically set through the AC-Link.

When a

rising edge is detected on either VOLUP# or VOLDW#, the MUTE bit is reset through the AC-Link.

The

Master Volume is set to the value before the Mute.

If the AC-Link is BUSY (when controlling the register from the AC’97 Control Register), the value in the

shadow register is set to AC’97 on the next frame.

The AC’97 Control Register is set to BUSY in this case.

When the master volume changes or is muted due to VOLUP#, VOLDW#, an interrupt is generated at the

host.

The interrupt is used to notify the driver that the Master Volume has been changed from the outside.

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