![Texas Instruments AM1808 Скачать руководство пользователя страница 1088](http://html.mh-extra.com/html/texas-instruments/am1808/am1808_technical-reference-manual_10945581088.webp)
X
Y
Z
Y
X
Y
X
M
Channel
1
Channel
2
W
W
Channel
2
Channel
1
B
Channel
2
W
Channel
1
M
M
Subframe 1
Subframe 2
Frame 191
Frame 0
Frame 1
1088
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Audio Serial Port (McASP)
24.0.18.2.3 Frame Format
An S/PDIF frame is composed of two subframes (
). For linear coded audio applications, the
rate of frame transmission normally corresponds exactly to the source sampling frequency f
s
. The S/PDIF
format clock rate is therefore 128 × f
s
(128 = 32 cells/subframe × 2 clocks/cell × 2 subframes/sample). For
example, for an S/PDIF stream at a 192 kHz sampling frequency, the serial clock is 128 ×
192 kHz = 24.58 MHz.
In 2-channel operation mode, the samples taken from both channels are transmitted by time multiplexing
in consecutive subframes. Both subframes contain valid data. The first subframe (
left
or
A
channel in
stereophonic operation and
primary
channel in monophonic operation) normally starts with preamble M.
However, the preamble of the first subframe changes to preamble B once every 192 frames to identify the
start of the block structure used to organize the channel status information. The second subframe (
right
or
B
channel in stereophonic operation and
secondary
channel in monophonic operation) always starts with
preamble W.
In single-channel operation mode in a professional application, the frame format is the same as in the 2-
channel mode. Data is carried in the first subframe and may be duplicated in the second subframe. If the
second subframe is not carrying duplicate data, time slot 28 (validity bit) is set to logical 1.
Figure 24-11. S/PDIF Frame Format