Intel 82801EB User Manual

AC ’97 Programmer’s Reference Manual 43 

 

 

The ICH5 AC ’97 controller provides support for 16- or 20-bit PCM out. Software can determine 
if 20-bit samples are supported in the controller by reading the sample capabilities bits in 
GLOB_STA registers as follows: MBBAR + 30h: Global Status Registers. 

23:22 

Sample Capabilities: Indicates the capability to support greater than 16-bit audio. 

00 = 16-bit Audio only supported (ICH1, ICH2, and ICH3 value) 

01 = 16 and 20-bit Audio supported (ICH5 value) 

10 = Reserved (for 24-bit audio support) 

11 = Reserved 

After determination of the controller capabilities, software can enable 20 –bits formats by 
programming the GLOB_CNT register as follows: MBBAR + 2Ch: Global Control Registers. 

23:22 

PCM Out Mode (POM): Enables the PCM out channel to use 16 or 20-bits. This does not affect 
microphone, microphone2, PCM In, PCM2 In, or S/PDIF DMA. When greater than 16-bits audio is 
used, the data structures are aligned as 32-bits per sample, with the upper order bits representing 
the data, and the lower order bits as don’t care. 
00 = 16 bit audio (default) 
01 = 20 bit audio 
10 = 24-bit audio (not supported. If set, indeterminate behavior will result. 
11 = Reserved. If set, indeterminate behavior will result.

 

 

Note:  Software must ensure that the PCM out DMA engine is stop and a new descriptor initialized 

before changing the value of PCM Out mode. These bits must not be modified when the PCM Out 
engine is running.