Datasheet

DD3V3

Input

DD3V3

Output

LMH0041, LMH0051

LMH0071, LMH0341

SNLS272Q –APRIL 2007–REVISED APRIL 2013

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• Allow for the output of a signal programmed by the SMBus

• Allow the monitoring of an external signal via the SMBus Monitor the status of the signal on input 1

• Monitor Lock condition of the input clock recovery PLL

GPIO

Functions

• Allow for the output of a signal programmed by the SMBus

• Allow the monitoring of an external signal via the SMBus

• Provides a constant clock signal

• LVDS TX Clock at 1/20 full rate

• CDR Clock at 1/20 full rate

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 GPIO

pin to monitor the status of the input signal on input 0, you would

load register 02h with the value 0010 0001b

Figure 14. Simplified LVCMOS Input Circuit Figure 15. Simplified LVCMOS Output Circuit

POTENTIAL APPLICATIONS FOR GPIO PINS

In addition to being useful debug tools while bringing a DES design up, there are other practical uses to which

the GPIO pins can be put:

Automatic Switching To Secondary Input If The Signal On The Primary Input Is Lost

By setting GPIO

to monitor the status of input0 when there is a signal present on input 0, the GPIO

pin will go

low when there is no signal present on the Input0 pin, if this signal is inverted and then used to drive the

RX_MUX_SEL then if the input on Input0 is lost, the device will automatically switch to Input1.

Another possible use of the GPIO pins is to provide access to external signals such as the CD output from an

equalizer or the LOCK output from the DES itself via the SMBus, helping to minimize the number of connections

between the DES and the FPGA.

Product Folder Links: LMH0041 LMH0051 LMH0071 LMH0341