CSC270 Homework 9

--D. Thiebaut 19:06, 8 April 2009 (UTC)

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UNDER CONSTRUCTION

Problem #1

Give the schematics for a 3-LED sequencer implemented with a 6811. This sequencer behaves very similarly to sequencers you designed with flipflops before Spring break. We will label one LED the green LED, another one the yellow LED, and the last one the red LED.

Show the 6811 assembly language program that will activate the LEDs in the following pattern: Green is ON for 1 second, then Yellow turns on for a second, then Red comes on for a second. And the cycle starts over with Green coming on. In other word, create a 3-state sequencer where each LED is ON in one state only.

Assume that we decided that Green should stay on for 2 seconds, Yellow for 1 second, and Red for 5 seconds, comment on the difficulty/complexity of modifying the original sequencer if the sequencer is implemented with flipflops, compared to the difficulty/complexity if the sequencer is implemented with a 6811.

Problem #2

Instead of wiring the 7442 as you did in the lab on 4/8/09, when you were implementing the 1-bit Output Port, assume that you had wired the 7442 to the 6811 in the following way:

• A3 of the 7442 is connected to A13 of the 6811
• A2 of the 7442 is connected to A14 of the 6811
• A1 of the 7442 is connected to A15 of the 6811
• A0 of the 7442 is connected directly to E of the 6811 (no inverter!)
• Ouput 3 of the 7442 (Pin 4) is connected to the clock input of the 74LS74 flipflop.

Will this design work? In other words, will the LSB of Acca get stored in the flipflop when the processor execute

         STAA 9000

Why, or why not? Explain thoroughly why it will or will not work.

Be careful, this is tricky! Use all the resources at your disposition to answer this question.