Although I unenable output, it still outputs 2.5 volt...

Sep 26, 2006 3 Replies
U

Hi, I am developing a data transmission circuit using the Cypress EZ-USB development kit. I have a question about setting register. When I unenable a certain pin, for example, CLKOUT pin, it have to be 0 Voltage, I think. But although the CLKOUT pin become to be float, it still outputs 2.5 Volt. Is it correct? Or, because of wrong firmware I made, it become to



2.5 Volt, not to 0 Volt? I am a beginner, so I have to study hard about USB. But if you help me, it is very helpful for me. Please teach me. Thank you for any help. Bye!!
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A

An output that is disabled will float to the voltage present at whatever it is connected to.

Also, since ones and zeros in TTL are defined as being > 2.7V or < 0.7V, it is neither a one nor a zero. It is "floating."

Al

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J

On Tue, 26 Sep 2006 12:54:43 GMT, Al wrote in comp.arch.embedded:

No, the logic levels in real TTL are = 2.0V for high.

Jack Klein Home: http://JK-Technology.Com FAQs for comp.lang.c http://c-faq.com/ comp.lang.c++ http://www.parashift.com/c++-faq-lite/alt.comp.lang.learn.c-c++ http://www.contrib.andrew.cmu.edu/~ajo/docs/FAQ-acllc.html
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A

No, check your data sheet. You're talking about "Recommended Operating Conditions." I'm talking about "DC Electrical Characteristics."

The actual levels depend upon your definition; is it Vih or Voh that you're talking about. He is asking about Voh and in the refernence, Voh is 2.4V .

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The actual value depends upon the testing conditions. On the data sheet I'm looking at, Voh for a commercial product is 2.7V .

Al

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