LMH0340SQE Datasheet, PDF (15/30 Pages) Texas Instruments – 3 Gbps, HD, SD, DVB-ASI SDI Serializer and Cable Driver With LVDS Interface

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LMH0040, LMH0050
LMH0070, LMH0340
SNLS271I – APRIL 2007 – REVISED APRIL 2013
Allow the monitoring of an external signal via the SMBus
Serializer Clock output
Bits 2 and 3 are used to determine the status of the internal pullup/pulldown resistors on the device—they are
loaded according to the following truth table:
00: pullup and pulldown disabled
01: pulldown enabled
10: pullup enabled
11: Reserved
Bit 1 is used to enable or disable the input buffer. If the GPIO pin is to be used as an output pin, then this bit
must be set to a ‘0’ disabling the output.
The LSB is used to switch the output between normal output state and high impedance mode. If the GPIO is to
be used as an input pin, this bit must be set to ‘0’ placing the output in high Z mode.
As an example, if you wanted to use the GPIO₀ pin to reflect the status of the LOCK pin, you would load the
appropriate register with the value 0001 0001b.
POTENTIAL APPLICATION FOR GPIO PINS
In addition to being useful debug tools while bringing a design up, there are other practical uses to which the
GPIO pins can be put:
Sensing if a cable is connected to an output –
When connecting the BNC cable to the output, connect the shield of the connector to GND via a
capacitor—making it an AC GND, but a DC open. Now connect that shield to one of the GPIO connections which
you configure as an input with a pullup. With no cable on the BNC, the GPIO pin will see a high state, but once a
terminated cable is connected, the shield will be brought down and you will read a low state.
V_DD
3.3V
V_DD
3.3V
p
p
Input
Output
n
n
Figure 12. Simplified LVCMOS Input Circuit
Figure 13. Simplified LVCMOS Output Circuit
Copyright © 2007–2013, Texas Instruments Incorporated
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