# Asynchronous Essay

529 WordsMay 6, 20133 Pages
[pic] Activity 3.2.2 SSI Asynchronous Modulus Counters Introduction In the last activity, we saw how easy it was to design asynchronous counters using either the D or J/K flip-flop. These designs had two big limitations. First, the count limit had to be a power of two (i.e., 2, 4, 8, 16, 32, etc.). All counts also started or ended at a count of zero. In the real world, we frequently need to set the count limit to some arbitrary value (10, 25, 85, etc.). More often than not, the starting or ending value will not be zero. For this reason we must design asynchronous modulus counters. An asynchronous modulus counter, or mod-counter, uses the addition of simple combinational logic to a standard asynchronous counter to set the count limit and starting point. In this activity we will simulate and build a Mod-5 counter that has a starting count of one. Equipment • Paper and pencil • Circuit Design Software (CDS) • Digital Logic Board (DLB) • Integrated Circuits o 74LS74 o 74LS10 o 74LS47 o Common Anode Seven-Segment Display • Resistors & Jumper Wires Procedure 1. The circuit shown below is a 3-Bit Mod-6 Up Counter implemented with 74LS74 D flip-flops. In this design the count will be displayed on a common anode seven-segment display using a 74SL47 encoder. This design will count from 0 to 5 and then repeat. [pic] 3-Bit Mod-6 Up Counter with D Flip-Flops a. Using the CDS, enter the 3-Bit Mod-6 Up Counter. Add a four-channel oscilloscope to monitor the signals Q0, Q1, Q2 and the output of the NAND gate. Run the simulation and capture a full count cycle (0-5) of the signal. Verify that the circuit is working as expected. If the results are not what are expected, review your circuit and make any necessary corrections. b. Adjust the time-base of the oscilloscope to zoom into the