Digital Electronics Principles Applications Amit Kumar Singh Counters

Digital Electronics Principles & Applications Amit Kumar Singh Counters

CHAPTER 8 PREVIEW • • • Overview of Counters Characteristics of Counters Ripple Up Counter Ripple Counter with Waveforms Ripple Down Counter Self-stopping Counter Frequency Division using Counters Using Counter ICs Magnitude Comparators Troubleshooting Equipment Troubleshooting Hints

OVERVIEW OF COUNTERS • Counter-by definition – One input (clock) – Outputs follow defined sequence • Common tasks of counter – Count up or down – Increment or decrement count – Sequence events – Divide frequency – Address memory – As memory

CHARACTERISTICS OF COUNTERS • Number of bits (4 -bit, 8 -bit, etc. ) • Maximum count – 4 bit = 24 = 0000 to 1111 in binary – 8 bit = 28 = 0000 to 1111 in binary • Modulus of counter-number of states – Decade counter – 4 -bit – 8 -bit • Up or down counter • Asynchronous or synchronous counter • Presettable counter • Self-stopping counter

RIPPLE COUNTER Binary Output Clock Input 00 1 10 10 1 Pulse 8 1 2 3 4 5 6 7 PS CLR input All 16 J-K flip-flops This Onand the 4 -bit next counter clockhas pulse (8) states all FFs and are in the will count toggle from because binary each 0000 will through receive 1111 INACTIVE TOGGLE MODE a H-to-L and then pulsereset one back after to another. 0000. Watch Thethe counter counthas ripple a modulus thru theof counter. 16.

RIPPLE COUNTER WITH WAVEFORMS Binary Output Clock Input 01 00 10 1 Pulse 5 1 2 3 4 Clock input FFs triggered on 1 s output H-to-L pulse. CLK toggles 1 s FF toggles 2 s FF. 2 s output 2 s FF toggles 4 s FF. 4 s output

DECADE COUNTER Binary Output Clock Input 111 ial c t i n I t 0 nt a ou 11 0 00 11 0 Pulse 8 1 2 3 4 5 6 7 Short negative pulse To clear input of each FF All J & K inputs = 1 All PR inputs = 1 To change mod-16 counter to decade counter: Count is at 1001. Reset count to 0000 after 1001 (9) count. Next clock pulse will increment counter for a When count hits 1010 reset to 0000. short time to 1010 which will activate the NAND gate See added 2 -input NAND gate that clears all and reset the counter to 0000. JK FFs to 0 when count hits 1010.

DOWN COUNTER 11 0 00 1 4 2 1 Pulse 5 3 Changes from Ripple Up Counter are wiring from Q’ outputs (instead of Q outputs) to the CLK input of the next FF. t oun c l a i Init t at se 111 y r a bin

SELF-STOPPING DOWN COUNTER 10 0 10 1 unt on tch coremained The Wacount. Pulse 8000. at binary 2 3 4 Pulse 8 1 5 6 7 This is a 3 -bit down counter. The 1 s FF is in TOGGLE mode when counting (J & K = 1). The 1 s FF switches to HOLD mode when the J and K inputs are forced LOW by the OR gate when the count decrements to 000. The count stops at 000.

COUNTER USED FOR FREQUENCY DIVISION 8 100 Hz 50 Hz 16 Clock Input 800 Hz 200 Hz 4 400 Hz 2

USING THE 7493 COUNTER IC • Counters are available in IC form. • Either ripple (7493 IC) or synchronous (74192 IC) counters are available. 100 ? Hz Hz 400 ? Hz Hz ? Hz 800 Hz 1600 Hz 7493 Counter IC wired as a 4 -bit binary counter

MAGNITUDE COMPARATOR A magnitude comparator is a combinational logic device that compares the value of two binary numbers and responds with one of three outputs (A=B or A>B or A<B). A(0) A(1) Inputbinary 0111 1111 0001 A(2) 74 HC 85 Magnitude Comparator A(3) B(0) B(1) Input binary 0110 0111 1100 B(2) B(3) A>B HIGH A=B HIGH A<B HIGH

TROUBLESHOOTING EQUIPMENT • • Logic Probe Logic Pulser Logic Clip (logic monitor) Digital IC Tester DMM/Logic Probe DMM or VOM Dual-trace Oscilloscope Logic Analyzer

SIMPLE TROUBLESHOOTING HINTS • Feel top of IC to determine if it is hot • Look for broken connections, signs of excessive heat • Smell for overheating • Check power source • Trace path of logic through circuit • Know the normal operation of the circuit