Broadcom BCM7405 - Audio Transmission Modes; Baseband BTSC Composite Output Mode; Sound if Output Mode; Table 1-15: RFM Audio Usage Modes for Normal Operation

2/24/2008 9T6WP
BCM7405 Preliminary Hardware Data Module
Functional Description 06/29/07
Broadcom Corporation
Page 1-58 RF Modulator Document 7405-1HDM00-R
Audio Transmission Modes
The RFM supports both monaural and stereo audio operation. More specifically, the RFM supports the following audio
transmission capabilities:
• MONO mode: Monaural transmission.
• STEREO mode: BTSC or NICAM stereo encoding and transmission.
• SAP mode: BTSC encoding and transmission of SAP (secondary audio program) without mono/main channel.
• DUAL MONO: BTSC or NICAM encoding and transmission of SAP simultaneously with a monaural signal.
Note that in BTSC mode, STEREO mode transmission and SAP mode transmission are mutually exclusive. The only BTSC
transmission mode that simultaneously transmits two different monaural audio streams is DUAL MONO.
The typical audio usage modes supported by the RFM are described in Table 1-15 along with the corresponding content of
the two PCM audio input channels that serve as inputs to the RFM.
• LEFT and RIGHT refer to a stereo pair produced by a stereophonic source (in MONO usage mode, LEFT, and RIGHT
can both be replaced by the same monaural source if no stereo source is available).
• MONO refers to monaural source.
• SAP refers to a monaural secondary audio program source (such as an alternate language source).
• X is used to refer to a don't care situation.
Baseband BTSC Composite Output Mode
The output of the RFM is normally an analog composite television signal. However, the FM modulator and mixer shown in
Figure 1-14 on page 1-56 may be bypassed so that the baseband BTSC encoder output may be sent directly to the RF
modulator’s DAC. In this mode, the digital video processor output is set to 0.
Sound IF Output Mode
The channel mixer shown in Figure 1-14 on page 1-56 may be optionally bypassed to output the sum of independently scaled
FM and NICAM carriers. For this video processor output is set 0.
Unsupported Audio Mode
In BTSC mode, simultaneous stereo and SAP transmission is not possible. Also the professional channel is not supported.
In NICAM mode, the data transmission feature is not supported.
Table 1-15: RFM Audio Usage Modes for Normal Operation
Usage Mode PCM Channel A PCM Channel B
MONO LEFT RIGHT
STEREO LEFT RIGHT
SAP X SAP
DUAL MONO MONO SAP