GS2970 Datasheet, PDF (87/145 Pages) Semtech Corporation – 3Gb/s, HD, SD SDI Receiver Complete with SMPTE Audio and Video Processing

4.19.3.5 Serial Audio Output Word Length
The audio output, in serial modes, has a selectable 24, 20 or 16-bit sample word length.
The ASWL[1:0] host interface register is used to configure the audio output sample word
length. Figure 4-23 shows the host interface 2-bit code for setting the audio sample word
length. When the presence of extended audio packets is detected in SD modes, the audio
de-embedder defaults to 24-bit audio sample word length.
Table 4-23: Audio Sample Word Lengths
ASWL[1:0]
Audio Sample Word Length
(SD)
Audio Sample Word Length
(HD)
00
24-bit
24-bit
01
20-bit
20-bit
10
16-bit
16-bit
11
Auto 24/20-bit (Default)
Reserved (Default)
NOTE: By default, at power-up, the word length is set to 12 bits. The desired word length
should be programmed through the host interface.
4.19.3.6 Audio Channel Status
The GS2970 detects the AES/EBU Audio Channel Status (ACS) block information for
each of the selected channel pairs.
ACS data detection is indicated by corresponding ACS_DET flag bits in the host
interface. The flag is cleared by writing to the same location.
4.19.3.6.1 Audio Channel Status Read
AES/EBU ACS data is available separately for each of the channels in a stereo pair. The
GS2970 defaults to reading the first channel of each pair. There are 184 bits in each ACS
packet, which are written to twelve 16-bit right-justified registers in the host interface.
The ACS_USE_SECOND bit (default LOW) selects the second channel in each audio pair
when set HIGH.
Once all of the ACS data for a channel has been acquired, the corresponding ACS_DET
bit is set, and acquisition stops. The ACS data is overwritten with new data when the
ACS_DET bit is cleared in the system.
4.19.3.6.2 Audio Channel Status Regeneration
When the ACS_REGEN bit in the host interface is set HIGH, the audio de-embedder
embeds the 24 bytes of the Audio Channel Status information programmed in the
ACSR[183:0] registers into the 'C' bit of the AES/EBU outputs. The same Audio Channel
Status information is used for all output channels.
In order to apply ACSR data;
• Set the ACS_REGEN bit to logic HIGH
• Write the desired ACSR data to the ACSR registers
• Set the ACS_APPLY bit to HIGH
GS2970 3Gb/s, HD, SD SDI Receiver Complete with
SMPTE Audio and Video Processing
Data Sheet
47478 - 4
September 2012
87 of 145