Rainbow Electronics MAX9671 - Manual (Page 24)

MAX9670/MAX9671
Low-Power Audio/Video Switch with Audio
Volume Control for Dual SCART Connectors
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on the same SCART pin, but not at the same time. The
75
Ω resistor connected to VCR_R/C_OUT must act as a
back termination resistor when the MAX9670/MAX9671
is transmitting chroma signal and as an input termina-
tion resistor when it is receiving a chroma signal. Figure
15 shows how the MAX9670/MAX9671 transmits a
chroma signal to the VCR SCART connector while
Figure 16 shows how the MAX9670/MAX9671 receives
a chroma from the VCR SCART connector.
Write a 0 into bit 2 of register 09h to open the pulldown
switch at VCR_R/C_OUT. To close the pulldown switch,
write a 0 into bit 6 of register 0Dh to turn off the output
amplifier, and then write a 1 into register 09h. See
Tables 17 and 18.
Figure 15. Gain-of-2 amplifier on VCR_R/C_OUT outputs chroma signal to VCR SCART connector. Notice that the pulldown switch on
VCR_R/C_OUT is open.
VCR
SCART
TV
SCART
A V = 2V/V
TV_R/C_OUT
A
V
= 2V/V
VCR_R/C_OUT
VCR_R/C_IN
BIAS
ENC_R/C_IN
BIAS
ENC_C_IN
BIAS
LPF
LPF
ON
MAX9670/MAX9671
75 Ω
75 Ω
0.1 µF
Figure 16. VCR_R/C_IN receives chroma signal from VCR SCART connector. Notice that the pulldown switch on VCR_R/C_OUT is
closed and that the gain-of-2 amplifier is off. The chroma signal from VCR SCART is looped through to the TV SCART in the above
configuration.
VCR
SCART
TV
SCART
A
V
= 2V/V
TV_R/C_OUT
A V = 2V/V
VCR_R/C_OUT
VCR_R/C_IN
BIAS
ENC_R/C_IN
BIAS
ENC_C_IN
BIAS
LPF
LPF
OFF
MAX9670/MAX9671
75 Ω
75 Ω
0.1 µF