Re: Confusion about ticks and tocks

Posted by WBahn on Feb 05, 2019; 9:15am
URL: http://nand2tetris-questions-and-answers-forum.52.s1.nabble.com/Confusion-about-ticks-and-tocks-tp4032821p4032837.html

Your phrase, "rising edge to the third vertical line (c) of the clock" is terribly vague.

Rising edge of what? What moment is that "rising edge" measured from? The third vertical line doesn't seem to have anything to do with the clock.

Most manufacturers define the propagation delay as the time from when the rising edge of the clock is halfway between LO and HI to when a changing output is halfway from prior state to new state.

Go look at some data sheets.

For instance, check out Section 7 of the TI data sheet for the 74HC74 Dual D-type FF.

http://www.ti.com/lit/ds/symlink/sn74hc74.pdf

As for why the book says what it does, remember that there are many different ways to build a flip flop and no one description, including the one I've given, can possibly describe them all.

The authors don't have ANY actual flip flops. They wrote a very simple, brain-dead simulator to emulate the basic functionality of a flip flop and ALL of the details of how it works inside are hidden from you. Their description is based on THEIR mental model of how THEIR flip flop behaves.