Home

rOm
Quest
Glossary

Random
Page
Search
Site
Lush
Sim
Class
Subject
Images

Help
FAQ
Sign
Up
Log
In
 AS Level     Sequential Logic     Synchronous Counter     >Up Counter and Reset<

# Sequential Logic Up Counter and Reset

Site for Eduqas/WJEC - Go to the AQA site.

AS Level    Sequential Logic    Questions 0 to 11   -->  View All

On the rising edge of the clock pulse, the input (D) is copied to the output (Q).
Since Q is connected to D, the output is inverted on the rising edge.

A ripple counter is an asynchronous counter where only the first flip-flop is clocked by an external pulse.
All subsequent flip-flops are clocked by the output of the preceding flip-flop.
The counter output might be momentarily wrong until the clock pulse has reached every the flip-flop.
This takes about 20 nanoseconds per flip-flop.

## A One Bit Counter using a D Type Flip Flop

In decimal this counts 0 1 0 1 0 1 and in binary, it's the same.

• The output of this counter has half the frequency of the input so this is also a frequency divider.
• The output has an exact 50:50 or one to one Mark Space Ratio, whatever shape the clock signal has.

View counter in the Lushprojects Simulator.

## A Two Bit Counter using Two D Type Flip Flops

In decimal, this counter counts 0 1 2 3 0 1 2 3 0 1 2 3 and in binary, 00 01 10 11 00 01 10 11 00 01 10 11 00 01 10 11 .

View counter in the Lushprojects Simulator.

## A Four Bit Counter with Reset - Alter it to reset on Ten

This counter goes from zero to five. On reaching six, a microsecond later it has reset to zero. Alter it to count up to nine. The reset should detect ten and cause the reset.

The AND gate is wired to detect six in decimal or in binary, 0 1 1 0. The gate output goes high and the flip flops all reset.

To reset on ten, the binary is 1 0 1 0 but beware! The flip flops are back to front in the diagram so you need 0 1 0 1 with bit values 1 2 4 8.

Subject Name     Level     Topic Name     Question Heading     First Name Last Name Class ID     User ID

 CloseEscapeX Q: qNum of last_q     Q ID: Question ID         Score: num correct/num attempts         Date Done

Question Text

image url

Help Text
Debug

• You can attempt a question as many times as you like.
• If you are logged in, your first attempt, each day, is logged.
• To improve your scores, come back on future days, log in and re-do the questions that caused you problems.
• In the grade book, you can delete your answers for a topic before re-doing the questions. Avoid deleting unless you intend re-doing the questions very soon.