cbtl12131 NXP Semiconductors, cbtl12131 Datasheet - Page 16

• Manufacturer Part Number: cbtl12131
• Description: Cbtl12131 Displayport Multiplexer For Bidirectional Video In All-in-one Computer Systems
• Manufacturer: NXP Semiconductors

NXP Semiconductors
CBTL12131
Product data sheet
7.8 AUX channel bias and termination
The AUX lines of Port B can be biased and terminated in accordance with the DisplayPort
Interoperability Guidelines in accordance with the configuration for either a sink or source,
depending on which is required. The control input for the termination and bias are CMOS
inputs AUX_TERM_SRC and AUX_TERM_SNK.
Together with the state of PATH_SEL and HPD_B_FLT (the filtered, steady state of
HPD_B), these signals allow a detection scheme by which the system controller can
resolve different connection scenarios of the external DisplayPort connector at Port B:
At first connection time, the latter scenario may appear identical to the first. In this case,
AUX_TERM_SNK (which applies a 500 kΩ pull-up on AUX_B_P line provided) can be
toggled HIGH in order to allow the other system to detect a connected sink, and configure
itself accordingly as a source.
Using AUX_TERM_SRC, the system controller is able to check whether the attached
device is a sink which is not asserting HPD (as some sinks will employ source detection
for power saving reasons). By applying the integrated 100 kΩ pull-up and pull-down
resistors, the attached sink will detect a source and assert its HDP when it is ready.
When HPD_B_FLT is HIGH, this means the attached device is asserting HPD and
CBTL12131 will activate its source type 100 kΩ termination resistors.
When PATH_SEL is HIGH, this means the internal DisplayPort sink (embedded panel) is
active, and its 1 MΩ termination resistors will apply the correct AUX bias to represent a
sink device.
In the default condition (PATH_SEL, HPD_B_FLT and AUX_TERM_SNK/SRC are all
LOW), 4.7 MΩ pull-down resistors are applied to the AUX_B pair, in order to avoid floating
conditions in case two similar systems are connected together.
When both AUX_TERM_SRC and AUX_TERM_SNK are HIGH, all integrated termination
resistors will be de-activated. For correct system operation, the system controller needs to
guarantee that AUX_TERM_SRC and AUX_TERM_SNK are never HIGH at the same
time, unless the external termination resistors are implemented.
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Nothing is connected
An external source is connected
An external sink is connected (either with or without source detection being performed
by the sink)
An external, second all-in-one system (using a topology similar or equivalent to
CBTL12131)
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 25 February 2011
DisplayPort multiplexer for bidirectional video
CBTL12131
© NXP B.V. 2011. All rights reserved.
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