I have been Learning about the IC-7490 Decade Counter which has 4 reset pins meaning 16 combinations, but the truth table can be compressed into just 4 Rows as I have done here: enter image description here

Is this fine or should I mention all the other combinations? What is recommended?

  • \$\begingroup\$ it says "others" all input states are covered. I'm guessing that the count pattern is discussed elsewhere in that document \$\endgroup\$ – Jasen Aug 26 '17 at 10:17
  • \$\begingroup\$ 'Don't care' states are perfectly valid. \$\endgroup\$ – Chu Aug 26 '17 at 11:09

Not as long as the information is unambiguous.

However, in your case, the R0(1) and R0(2) do not matter at all. If you remove them from the table you will get the same formula at the end when working out the table to the formula.

If you would put the entire table, you will also get the same formula. So you just made already some assumptions (for the X). Your table is halfway making the formula already, which is no problem at all. It saves you some time not to put all 16 combinations.

You better can start with the entire table if you cannot trivially make the assumptions you made (e.g. the X-es which can be either 0 or 1).


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.