1 Introduction
In this lab you will write a task to read the Analog-to-Digital (ADC) and display the results on the OLED. You will use the FreeRTOS framework from Lab #4.
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1.1 Program Modifications
Make a copy of the FreeRTOS_LM3S1968 project from Lab #4 and rename appropriately, e.g. FreeRTOS_LM3S1968_ADC. You will add your task to this copy as described below.
1.2 ADC Background
The operation of the Analog-to-Digital converter was described in class. The steps to program the ADC and sample the analog input were discussed in class and a sample task was provided. Additional information on the ADC hardware and DriverLib software are at:
http://www.ittc.ku.edu/~gminden/Embedded_Systems/PDFs/TI_Stellaris_LM3S1968 _EvalBoard.pdf,
http://www.ittc.ku.edu/~gminden/Embedded_Systems/PDFs/TI_Stellaris_LM3S1968. pdf, and
http://www.ittc.ku.edu/~gminden/Embedded_Systems/PDFs/TI_Stellaris_DriverLib.p df.
Information on FreeRTOS APIs is at:
http://www.freertos.org
You should read those documents.
1.3 Connector Pin-outs
With the LM3S1968 evaluation board receptacle facing you, we will use twenty pins on the left-hand side to connect to off-board circuits. These pins are:
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Pin
Signal
Notes
66
ADC<7
65
Gnd
64
ADC<5
63
ADC<6
62
ADC<0
Used for potentiometer
analog input. See
example.
61
ADC<4
60
ADC<2
59
ADC<1
58
Gnd
57
ADC<3
56
PD<0/IDX<0!
55
Gnd
54
PD<2/U1RX!
Used to discharge
capacitor.
53
PD<1/PWM<1!
52
PG<3
51
PD<3/U1Tx!
50
PG<1/U2Tx!
49
PG<2/PWM<0!
48
PC<7/C2!
-
47
PG<0/U2Rx!
These signals and pin numbers were extracted from the schematics of the
LM3S1968 evaluation board available in:
http://www.ittc.ku.edu/~gminden/Embedded_Systems/PDFs/TI_Stellaris_LM3S1968 _EvalBoard.pdf.
1.4 Off-board Circuit
The initial off-board circuit will be a potentiometer. The circuit is:
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Vdd = 3.3 VDC. As you turn the potentiometer your ADC readings should vary between 0 and 1,023.
A description of the expansion board is at:
http://www.ittc.ku.edu/~gminden/Embedded_Systems/Laboratory/EECS_388_Sensor Orientation_B70224.pdf.
1.5 New Task
Write a new task to sample ADC<0 (ADC channel 0) and display the measurement value on the OLED. The task steps are:
Initialize ADC0, Sequencer 0, to sample ADC channel 0 under processor control (e.g. Processor_Trigger) (See lecture slides.).
Insure the OLED display is initialized.
Sample ADC0/Ch0 once per second.
Write the measurement value to the OLED display using the format: "ADC: xxxx" starting at column 0 and an appropriate row.
Repeat steps 3 and 4 once per second.
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