13-04-2012, 04:14 PM
Counters and Registers
ch07.ppt (Size: 197 KB / Downloads: 114)
Introduction
Chap.
How FFs and logic gates can be combined to produce different types of counters and registers
Divided into 2 parts
Part I : principles of counter operation, various counter circuit arrangement, and
representative IC counters
Part II : counter application, types of IC register, and troubleshooting
Asynchronous(Ripple) Counters
Asynchronous Counter : Fig. 7-1
The FFs do not change states in exact synchronism with the applied clock pulses
Ripple Counter
The FFs respond one after another in a kind of rippling effect
The terms asynchronous counter and ripple counter interchangeably
Synchronous(Parallel) Counter
Synchronous/Parallel Counters
All of the FFs are triggered simultaneously (in parallel) by the clock input pulses
Synchronous MOD-16 Counter : Fig. 7-17
Circuit Operation
Each FF should have its J and K inputs connected
such that they are HIGH only when the outputs of
all lower-order FFs are in the HIGH state
Presettable Counters
Presettable Counter/Parallel Loading Counter
Preset to any desired starting count either asynchronously or synchronously
Presettable Parallel Counter with Asynchronous Preset : Fig. 7-19
The counter is loaded with any desired count at any time
Decoding a Johnson Counter
For a given MOD number, a Johnson counter requires only half the number of FFs that a ring counter requires
MOD-8 Ring Counter : 8 FFs
MOD-8 Johnson Counter : 4 FFs
Ring Counter does not require decoding gates