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Bachelor's Degree in Telecommunications Systems and in Network Engineering |
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Chapter 3 problems |
- B3.10 - |
4-bit radix-2 /Johnson and 8-bit Johnson / radix-2 converters |
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1.- Specifications
Design the 4-bit binary radix-2 to Johnson code converter represented in Fig. 1 using a PIC18F4520 microcontroller, C language and Microchip IDE tools. Test your design using Proteus. Add switches to input codes and enable signals and LED to visualise the operations.
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Fig.1. Symbol of the 4-bit binary to Johnson converter. |
The same project is proposed in D1.10 as a combinational circuit based on logic gates. The emphasis is focused therefore in learning how to poll/read digital inputs and write digital outputs. The truth table will be solved using a behavioural plan B interpretation translated into C language and organising the hardware-software diagram so that the input and outputs variables will be saved in RAM memory in an infinite loop.
Draw an example timing diagram.
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Fig. 2. Timing diagram example. |
2. Planning
You will solve the circuit in several steps, adding a few lines of code each time to develop and test immediately to debug any error before adding more code. For instance:
- step #1 read only E and monitor its current value var_E in a watch window.
- step #2 read the vector B(3..0) and monitor its current value in a watch window. In this way, your read_inputs() function will be validated.
- step #3 Imagine a given value for the variable var_J, write it in the corresponding pins and observe LED values, thus validating your function write_outputs().
- step #4 complete the truth table and the project.
A) Planning hardware
Copy and adapt a circuit from any of the LAB9 projects and name it Bin_Johnson_4bit.pdsprj. Assign pins to inputs and outputs accordingly to one of the following options (your instructior will tell you which):
Pin assignment option #1:
E --> RB5; B(3..2) ---> RC(1.0); B(1..0) ---> RC(7..6); J(7..4) ---> RA(3..0); J(3..2) ---> RB(7..6); J(1..0) ---> RD(4..3)
Pin assignment option #2:
E --> RB2; B(3..2) ---> RD(1.0); B(1..0) ---> RD(7..6); J(7..4) ---> RB(6..3); J(3..2) ---> RA(3..2); J(1..0) ---> RC(4..3)
Pin assignment option #3:
E --> RC5; B(3..2) ---> RC(1.0); B(1..0) ---> RD(5..4); J(7..4) ---> RA(4..1); J(3..2) ---> RB(5..4); J(1..0) ---> RB(7..6)
Project location:
C:\CSD\P9\Bin_Johnson_4bit\(files)
B) Planning software
Organise the main program in our CSD way. Copy and adapt a circuit from any of the LAB9 projects and name it Bin_Johnson_4bit.c.
Propose a hardware-software diagram naming all the electrical signals, RAM variables and the software functions.
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Fig. 3. Hardware-software diagram. |
Describe all the RAM memory variables used in this project and its type.
Explain how to configure the µC in init_system().
Organise using a flowchart the interface function read_inputs().
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Fig. 4. Reading inputs. |
Organise using a flowchart the interface function write_outputs().
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Fig. 5. Writing outputs. |
Infer the truth_table() software function using a behavioural plan B interpretation from the corresponding flowchart.
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Fig. 6. Bin_Johnson_48bit initial discussion on adapting the truth table using plan B flowcharts. |
3. Developing & 4. Testing (debugging)
- Step #1. Write the Bin_Johnson_4bit.c source code translating the function flowcharts. Start capturing only one input as in (LAB9) and visualising it in the watch window as a RAM variable as indicated in the sequence of steps above in the planning section. And only then go to the next step developing & testing more inputs.
Start a software IDE project for the target microcontroller PIC18F4520 and generate the configuration files ".cof" and ".hex" after compilation. Discuss the project summary: % of ROM used for the code, number of RAM bytes used, etc.
| Note: Step-by-step tactical approach for developing and testing the project: Read one input at a time and run to check that the voltage value is correctly captured as a valid digital value in RAM memory. Write one output at a time and run to check that your code is correct to light the LED connected at the output pin. |
Add a few lines of code every time, compile and run the test intereactively to check results watching variables.
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Fig. 7. Example pictures demonstrating how the circuit works. |
Measure how long does it take to run the main loop code when using a 4 MHz and a 16 MHz quartz crystal oscillator.
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Fig. 8. Loop execution time measurements. |
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Chapter 3 problems |
- B3.10 - |
4-bit radix-2 /Johnson and 8-bit Johnson / radix-2 converters |
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1.- Specifications
Design the 8-bit Johnson to binary radix-2 code converter represented in Fig. 1 using a PIC18F4520 microcontroller, C language and Microchip IDE tools. Test your design using Proteus. Add switches to input codes and enable signals and LED to visualise the operations.
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Fig.1. Symbol of the Johnson_bin_8bit converter. |
The same project is proposed in D1.10 as a combinational circuit based on logic gates.
The emphasis is focused therefore in learning how to poll/read digital inputs and write digital outputs. The truth table will be solved using a behavioural plan B interpretation translated into C language and organising the hardware-software diagram so that the input and outputs variables will be saved in RAM memory in an infinite loop.
Draw an example timing diagram.
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Fig. 2. Timing diagram example. |
2. Planning
You will solve the circuit in several steps, adding a few lines of code each time to develop and test immediately to debug any error before adding more code. For instance:
- step #1 read only E and monitor its current value var_E in a watch window.
- step #2 read the vector J(7..0) and monitor its current value in a watch window. In this way, your read_inputs() function will be validated.
- step #3 Imagine a given value for the variable var_Bin, write it in the corresponding port pins and observe LED values, thus validating your function write_outputs().
- step #4 complete the truth table and the project.
A) Planning hardware
Copy and adapt a circuit from any of the LAB9 projects and name it Johnson_bin_8bit.pdsprj. Assign pins to inputs and outputs accordingly to one of the following options (your instructior will tell you which):
Pin assignment option #1:
E --> RB5; J(7..4) ---> RA(3..0); J(3..2) ---> RB(7..6); J(1..0) ---> RD(4..3); B(3..2) ---> RC(1.0); B(1..0) ---> RC(7..6)
Pin assignment option #2:
E --> RB2; J(7..4) ---> RB(6..3); J(3..2) ---> RA(3..2); J(1..0) ---> RC(4..3); B(3..2) ---> RD(1.0); B(1..0) ---> RD(7..6)
Pin assignment option #3:
E --> RC5; J(7..4) ---> RA(4..1); J(3..2) ---> RB(5..4); J(1..0) ---> RB(7..6); B(3..2) ---> RC(1.0); B(1..0) ---> RD(5..4)
Project location:
C:\CSD\P9\Johnson_bin_8bit\(files)
B) Planning software
Organise the main program in our CSD way. Copy and adapt a circuit from any of the LAB9 projects and name it Johnson_bin_8bit.c.
Propose a hardware-software diagram naming all the electrical signals, RAM variables and the software functions.
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Fig. 3. Hardware-software diagram. |
Describe all the RAM memory variables used in this project and its type.
Explain how to configure the µC in init_system().
Organise using a flowchart the interface function read_inputs().
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Fig. 4. Reading inputs. |
Organise using a flowchart the interface function write_outputs().
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Fig. 5. Writing outputs. |
Infer the truth_table() software function using a behavioural plan B interpretation from the corresponding flowchart.
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Fig. 6. Johnson_bin_8bit initial discussion on adapting the truth table using plan B flowcharts. |
3. Developing & 4. Testing (debugging)
- Step #1. Write the Johnson_bin_8bit.c source code translating the function flowcharts. Start capturing only one input as in (LAB9) and visualising it in the watch window as a RAM variable as indicated in the sequence of steps above in the planning section. And only then go to the next step developing & testing more inputs.
Start a software IDE project for the target microcontroller PIC18F4520 and generate the configuration files ".cof" and ".hex" after compilation. Discuss the project summary: % of ROM used for the code, number of RAM bytes used, etc.
| Note: Step-by-step tactical approach for developing and testing the project: Read one input at a time and run to check that the voltage value is correctly captured as a valid digital value in RAM memory. Write one output at a time and run to check that your code is correct to light the LED connected at the output pin. |
Add a few lines of code every time, compile and run the test intereactively to check results watching variables.
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Fig. 7. Example pictures demonstrating how the circuit works. |
Measure how long does it take to run the main loop code when using a 4 MHz and a 16 MHz quartz crystall oscillator.
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Fig. 8. Loop execution time measurements. |
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