# A 2 in one question

Discussion in 'Homework Help' started by mannik, Dec 1, 2004.

1. ### mannik Thread Starter New Member

Nov 26, 2004
3
0
I have some problems understand this (again) the book and my teacher is not of much help so I try here.

This circut here: http://empty-site.org/flip1.jpg is a flip-flop which is triggered on the rising edge, I have to change it so it's triggered on the falling edge but I can't find any info regarding that.

I also need to find out of following:

I have a 4X3 memory it uses 22 AND gates and 3 OR gates, how do I calculate how many AND / OR gares needed in a 256 X 8 memory ?

I will be very thankfull for the help I can get, last time I was very lucky!

tommy

2. ### Steel Member

Oct 27, 2004
25
0
Looking at the schematic, I BELIEVE (someone correct me if I am wrong) that there is a problem with the logic on the clock pulse (you will never activate that AND gate.)

...To switch the clock pulse in that part of the circuit, you can change the AND to a NAND....

but something doesn't strike me as solved...hopefully someone else will chime in.

3. ### WildZBill New Member

Dec 18, 2004
6
0
Actually that clock circuit turns a square wave into a short positive pulse. The inverter introduces a very slight delay. The positive signal reaches the bottom input instantly, while the top input is still positive until the signal propagates through the inverter.
Place an inverter at the input of that circuit to change to a trailing edge trigger.

For the memory question, I would have to see the 3X4 circuit before I could guess at the larger circuit. It is not scalable since 2048 is not divisible by 3.