UPC EETAC Bachelor's Degree in Telecommunications Systems and in Network Engineering EEL

Chapter 3 problems

      - B3.3 -

5-bit ones counter  (μC - C)

Problems

B3.2

B3.4

1. Specifications

Design the 5-bit ones counter represented in Fig. 1 using plan B and a microcontroller PIC18F4520.

The same project is proposed in D1.3 as a combinational circuit based on logic gates.

Ones counter circuit

Fig.1. Ones_counter_5bit symbol. 

Use this project to review basic concepts on μC as theory attached to the specifications section.

 

2. Planning

A) Planning hardware

Copy and adapt a circuit from any of the previous projects (LAB9) and name it Ones_Counter_5bit.pdsprj. Assign pins to inputs and outputs accordingly to one of the following options (your instructior will tell you which):

Pin assignment option #1:

D4 --> RC7; D3 --> RC4; D2 --> RC3; D1 --> RB6; D0 --> RA1

Y2 --> RA2; Y1 --> RB5; Y0 --> RB0

Pin assignment option #2:

D4 --> RB5; D3 --> RB3; D2 --> RC2; D1 --> RC0; D0 --> RA0

Y2 --> RA3; Y1 --> RC5; Y0 --> RD0

Pin assignment option #3:

D4 --> RD7; D3 --> RD3; D2 --> RB3; D1 --> RA1; D0 --> RB2

Y2 --> RD6; Y1 --> RC5; Y0 --> RB1

Project location:

C:\CSD\P9\Ones_Counter_5bit\(files)

B) Planning software

Organise the main program in our CSD way.

Propose a hardware-software diagram naming all the electrical signals, RAM variables and the software functions.  

Explain how to configure the µC in init_system(). List all RAM variables required and their type.

Organise using a flowchart the interface function read_inputs().

Organise using a flowchart the interface function write_outputs().

Infer the truth_table() software function using a behavioural interpretation and the corresponding flowchart.

 

Developing & testing (debugging)

Write the Ones_Counter_5bit.c source code translating the function flowcharts. Start capturing only one input as in (LAB9) and visualising it in the watch window. And only then go step by 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.

Add a few lines of code every time, compile and run the test intereactively to check results watching variables.

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.

Measure how long does it take to run the main loop code when using a 4 MHz and a 20 MHz crystall oscillators.