Datasheet

LP
Priority
HPD_A
0
1
0
1
0
1
HPD_B
0
1
HPD_OUT
0
1
Channel A
Z
0
1
ChannelB
0
1
HI-Z
DATA
LP
Priority
HPD_A
0
1
0
1
0
1
HPD_B
0
1
HPD_OUT
0
1
Channel A
Z
0
1
ChannelB
0
1
HI-Z
DATA HI-Z
DATA
SN75DP122A
www.ti.com ............................................................................................................................................................................................ SLLS939 – NOVEMBER 2008
Figure 43.
– Case two: In this case the HPD input that is initially HIGH is not the port with priority. When the HPD input
of the port that has priority goes high, the HPD output is forced LOW for some time in order to simulate
an unplug event to the source device. The duration of this LOW output is defined as t
T2(HPD)
. If the HPD
input of the port with priority pulses LOW for a short duration while the t
T2(HPD)
timer is counting down, the
timer is reset. Once this time has passed the switch switches to the port with priority and the output HPD
once again follows the state of the newly selected channel ’ s HPD input (see Figure 44 ).
Figure 44.
4. 4. Priority pin is toggled. There are also two possible starting cases for this scenario:
– Case one: In this case only one HPD input is HIGH. A port whose HPD input is LOW cannot be selected.
In this case, the state of the priority pin has no effect on the switch (see Figure 45 ).
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