Microsoft Word - Digital Logic Design v_4_6a

 Additional Types of Shift Registers:
 Parallel in/Parallel out
 Parallel in/Serial out
 Serial in/Parallel out
 Serial in/Serial out

 Additional Types of Counters:
 Ring Counters; a 1 is shifted through each flip-flop while all the other flip-flop outputs are 0.
(one hot encoding is a recommended design)
 Twisted Ring Counters (or switch tail ring counter, Johnson counter, mobius counter)
 Linear Feedback Shift Register Counter (or maximum length shift counters)
Depending on design it will count all possible states, but skips all 0s and 1s states.

Recommendation: Reader is encouraged to explore full definition of these counters and others

through independent research.

 Adding an Enable Input
It may be necessary to stop the count at times and then continue counting. In this section we will
design a “Full-Encoded Stoppable Counter”. This counter will count up as long as EN is asserted;
otherwise it will stop the counting.

GND

Vcc=+5V

Diode

Schmitt

Trigger

Vc CLR CLR’

C=10 uF

R=10 K Ω

On

Vcc

Off

5V

Vc

0V

H

CLR

L

H

CLR’

L

RC with C grounded

GND

Vcc=+5V

Vc CLR’ CLR

C=10 uF

On

Vcc

Off

5V

Vc

0V

H

CLR’

L

H

CLR

L

RC with R grounded

R=10 K Ω

Power is off   Power is on

Time it takes the Vc = 5(1- e –^ t/RC )^

to trigger the Schmitt trigger

Time it takes the Vc = 5 (e –^ t/RC^ ) to

trigger the Schmitt trigger