YMF724F
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.
Push SW
1k
VOLUP#
Push SW
1k
VOLDW#
1000p
1000p
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
register automatically updates the AC’97 master volume register through the AC-Link.
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
register automatically updates the AC’97 master volume register through the AC-Link.
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.
January 14, 1999
-41-
YAMAHA [ YAMAHA CORPORATION ]
