I am trying to connect the O/P from TCXO (FOX Electronics FOX924B. 20 MHz, 2.5 PPM, 3.3 V supply, Output HCMOS VOL = 0.5 V and VOH = 80% of VDD) to 74HC240 buffer, which I am also running at 3.3 V.

I am not getting anything at the output of the buffer. But as per the datasheet of 74HC240 from Motorola, it is capable of running at 3.3 V. Where I am making the mistake? I will provide any further data, circuit diagram if required.

  • \$\begingroup\$ There's an output enable on the buffer, is that driven? Have you verified the TCXO is oscillating with an oscilloscope? You will get better responses if you add a circuit diagram. \$\endgroup\$ – Colin Aug 10 '20 at 14:36
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    \$\begingroup\$ Yes, the diagram is required. Is the buffer enabled with the output enable pin? \$\endgroup\$ – Justme Aug 10 '20 at 14:38
  • \$\begingroup\$ Are you getting anything at the input of the buffer? \$\endgroup\$ – user253751 Aug 10 '20 at 14:49
  • \$\begingroup\$ It was my mistake. I did not grounded the output enable lines. What a silly mistake. Now it working fine. Great support guys. \$\endgroup\$ – Ashok Das Aug 10 '20 at 15:44

Buffer output must be enabled to see anything on the output. Ground the OE pin to enable it.


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