Figure 6-4. Audio Subsystem; Table 6-1. Audio Moded - Compaq EN Series Technical Reference Manual

Chapter 6 Audio Subsystem
6.2.1.3 PCM Configuration Modes
PCM operation can be configured for compatible ( common sound board functionality) mode or
set up for extended mode, which has some performance advantages. Table 6-1 lists the
differences between the modes of operation.
Table 6–1. Audio Mode Differences
Function
FIFO Size Available
Mono 8-bit ADC, DAC
Mono 16-bit ADC, DAC
Stereo 8-bit ADC, DAC
Stereo 16-bit ADC
Stereo 16-bit DAC
Signed/Unsigned Control
AGC During Capture
Programmed I/O Block Transfer
FIFO Status Flags
Auto Reload DMA
Time Base for Programmable Time
ADC/DAC Jitter
Sound Blaster Pro Compatible
6.2.1.4 PCM Bus Cycles
The I/O and DMA cycles used by PCM operations to process .WAV data follow standard ISA bus
conventions. All bus transfers occur at the bytes level. Programmed I/O cycles are always used
for programming the control registers and may also be used for transferring audio data to and
from the audio subsystem as well. Quantized audio data is built using the "little endian" format
(LSB occupies the lowest memory address). Data transfers over the ISA occur as shown below.
8-bit Mono
8-bit Stereo
16-bit Mono
16-bit Stereo
Figure 6–4. Audio Subsystem-to-ISA Bus PCM Audio Data Formats / Byte Ordering
6-6 Compaq Deskpro EN Series of Personal Computers
Desktop and Minitower Form Factors
Table 6-1.
Audio Mode Differences
64 bytes (SW Control)
44 KHz Max Sampling
22 KHz Max Sampling
22 KHz Max Sampling
11 KHz Max Sampling
Mono Only (22 KHz)
1 MHz or 1.5 MHz
31
Sample 6 Sample 5 Sample 4
Sample 3 Sample 3 Sample 2
Right Left Right
Sample 3
Mono Hi Mono Lo Mono Hi
Sample 3
Left Hi Left Lo Right Hi
Third Edition - September 1998
Compatibility
Mode
256 bytes (HW Control)
n/a
No
No
No
Yes
+/- 2 usec
Yes
24 16 8
Sample 3 Sample 2
Sample 2 Sample 1
Left Right
Sample 2 Sample 1
Mono Lo Mono Hi
Sample 1
Sample 2
Right Lo Left Hi
Extended
Mode
44 KHz Max Sampling
44 KHz Max Sampling
44 KHz Max Sampling
44 KHz Max Sampling
44 KHz Max Sampling
Yes
No
Yes
Yes
Yes
800 KHz or 400 KHz
None
No
0
Sample 1
Sample 1
Left
Mono Lo
Left Lo
Time