March 1, 2000 page 1 S. Derenzo
Solutions for Midterm #1 - EECS 145M Spring 2000
1a
µComputer
8-bit input port
8-bit output port
LED
44 Ω
buffer amp
push button switch
5V
0.6 V, 0.1 A
The push button should be connected to the input port and the LED should be driven by the output
port and amplifier.
[2 points off for no series resistor to limit LED current]
[1 point off if resistor shown but value not given]
[3 points off if input and output ports not shown]
1b.
1Computer waits for button to be pressed
2User presses the button, grounding the input line
3Computer senses low signal
4Computer uses system clock to wait a random 5-10 sec time
5Computer puts output line to amplifier high
6Computer reads system time T1 (ms)
7LED lights
8Computer waits for low input line
9Human recognizes LED and presses button a second time
10 Computer recognizes low line and reads system time T2
11 Computer subtracts system times (T2 - T1), converts to seconds, displays and stores results,
and turns off LED
[2 points if hardware steps such as button press and LED lighting not given]
[2 points off if time difference not calculated and stored]
2
Set
Reset
5 V µComputer
8-bit input port
8-bit output port
latch
1 kΩ
Te essential features of the solution are (1) button sets latch (2) latch output goes to computer input
port (3) output port resets latch [3 points off for each missing feature]
