Description
1 8051 Micro-controller Programming using Edsim51
In this assignment, you are going to write a program and simulate a motor revolution counter using a
8051 micro-controller, DC motor, and LCD in Edsim51.
Here in Figure 1, DC motor panel and LCD (8051 peripherals in Edsim51) are highlighted in red boxes.
The motor can be disabled/enabled by clicking on the motor Enabled/Disable button.
Figure 1: Edsim51
1.1 The Motor
A DC motor is a rotatory instrument that works on DC power to convert electrical energy into mechanical
energy. DC motors can vary in size and power from small motors in toys and appliances to large
mechanisms that power vehicles, pull elevators and hoists, and drive steel rolling mills, etc.
Figure 2 shows how the DC motor may be interfaced with the 8051 in the Edsim51 simulator. P3.0 and
P3.1 are applied to a dual bridge driver, the outputs of which are applied to a bi-directional DC motor.
The truth table for the bridge and its effect on the motor is shown in Table 1.
Table 1: Truth table for the bridge driver
1
Figure 2: Schematic of interfacing Motor with 8051
Note: The motor control lines share the TXD and RXD lines for the 8051’s internal serial port. As can
be seen in the Figure 2, these lines are also connected to the external UART. Therefore, when exercising
the motor, garbage messages may appear in the UART’s receiver window.
The motor sensor, which is applied to P3.5, goes low once every revolution (in the simulator, whenever
the motor shaft lines up with the sensor (positioning at 12 o’clock), the sensor changes from black to red
and P3.5 goes to logic 0). P3.5 is the external clock source for timer 1. Therefore, code can be written
that, using timer 1, counts the motor’s revolutions. The speed of the motor can be varied manually
from MIN to MAX (using the slider to the right of the motor – take a look at the hardware screenshots
above). This will make the revolution counting programs more interesting.
1.2 Motor Revolution Counter
The motor should be setup to rotate in a clockwise (forward) direction and the number of revolutions
per second should be displayed on LCD. It needs to be observed if the number of revolutions per second
increases or decreases (LCD gets updated) as the motor slider (see Figure 1) is moved up (toward MAX)
or down (toward MIN).
The motor sensor is connected to P3.5 (see Figure 2), which is the external clock source for timer 1.
Therefore, timer 1 is put into event counting mode and counts how many revolutions have taken place.
To get the number of revolutions per second (RPS), one must inspect the revolution count in timer 1
every second, convert it to decimal, and display it (in decimal) on the LCD panel and then reset the
count. This process should be repeated endlessly. Due to the limited bit precision (8 bit registers), we
will approximate RPS by inspecting timer 1’s count every 10ms (instead of doing so every second), and
multiplying that count by 100 (100=1second/10ms). One way to do this is to have interrupts occur
every 10ms. Another way is to have the microcontroller continually checking if 10ms have elapsed. In
either case, when 10ms have elapsed, the microcontroller should initiate a ”Hex to Decimal” conversion
of the revolution count. When the conversion is complete, the LCD is updated with new value. At this
time, the previous revolution count should be cleared and counting should be started again.
Note: The result of conversion (from Hex to Decimal) shows the number of motor revolutions in one
2
second, which can be approximated by multiplying the 10ms revolution count by 100.
1.3 LCD
LCD should be connected to port P1 of 8051, and Set Interface data length to 8 bits, 2 line, 5×7 character
font, also set the entry mode to increment with no shift. The display should be updated once the slider
has moved up or down. Make sure to use P3.2 for LCD E and P3.3 for LCD RS in your
program and Edsim51 pin configuration.
1.4 Testing Your Program
Run your program with the motor at different speeds (use the slider to the right of the motor to increase
the motor speed). The LCD should display the number of motor revolutions per second in 5 decimal
digits. You can run your program with updating frequency from 1 to 100. Submit 3 screenshots of your
program changing the motor slider in different speeds.
2 Assignment Deliverable
– Your code should be commented.
– Submit your assembly file along with 3 screenshots (mentioned in Section 1.4) through Canvas before
deadline in a .zip file.
