Specifications

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ESS Technology, Inc. SAM0025A-062397 15

ES1879 DATA SHEET

DRQ LATCH FEATURE

PRELIMINARY

A pop may be heard if the DAC level was left at a value

other than mid-level (code 80h on an 8-bit scale) by the

previous play operation. To prevent this, always finish a

DAC transfer with a command to set the DAC level to mid-

range:

10h + 80h

DRQ LATCH FEATURE

The DRQ latch feature is enabled when bit 7 of Vendor-

Defined Card-Level register 29h is high (see Figure 6).

If this feature is enabled, each of the four audio DRQs will

be latched high until one of the following occurs:



A DACK low pulse occurs while DRQ is low or if DRQ

goes low due to a DACK pulse.



A hardware reset occurs.



8-16 milliseconds elapse while DRQ is low.

Figure 6 DRQ Latch

FOURTH DRQ CHANNEL

The ES1879 supports an optional fourth DMA channel

using pins DRQD and DACKBD. Connecting these pins to

an ISA DMA channel is optional.

If DRQD and DACKBD are not connected to an ISA DMA

channel, program bits 7:4 of PnP Vendor register 24h to be

2h (0010). In this case, pin 80 is available as GPI1

(general-purpose input 1) and pin 90 is available as either

the active-low hardware volume control MUTE input or as

GPI4 (general-purpose input 4).

If bits 7:4 of PnP Vendor register 24h are other than 2h,

then pin 80 is assumed to be connected to an ISA DRQ pin

and is not available as GPI1 (if GPI1 is read, it appears to

be 1 all the time). Likewise, pin 90 is assumed to be

connected to an ISA DACK pin and is not available to be

used as a hardware volume MUTE input or GPI4. If a mute

function is desired, program mixer register 64h so that the

combination of both VOLUP and VOLDN pins low together

acts as a mute command.

Normally, DRQA/DACKBA is connected to DMA channel

0, DRQB/DACKBB is connected to DMA channel 1, and

DRQC/DACKBC is connected to DMA channel 3. This

leaves one of the three 16-bit channels for DRQD/

DACKBD. Since the ES1879 only has 8 data lines, the

Windows driver will arrange the data so that a 16-bit

channel can be used for 8-bit data. For this reason, the

DRQD/DACKBD channel should only be used for the

second DAC playback channel and not the game-

compatible first channel.

The DRQ latch feature is enabled when bit 7 of Vendor-

Defined Card-Level register 29h is high (see Figure 6).

DRQ

125 Hz

-DACK

-RESET

AND

DRQ Out