Basic of Firmware & Embedded Software Programming in C

1. General Drivers
Embedded Systems

3. Agenda
• What is Generic Drivers
• Digital Input and Output Ports
• Keys
• Key Matrix
• LEDs
• LED Matrix
• PWM Outputs
• Displays
• Seven Segments Displays
• Alphanumeric LCDs
• EEPROM Interface
• RS232 vs RS485

4. Key Input
• We can use the microcontroller, GPIO to detect the key input signal. We need to
configured the microcontroller pin/port as input port. Here in above example
microcontroller pin (port 7 bit 0) P70 is used to capture the input. Consider when
switch is not pressed (OFF), the value at microcontroller pin will be HIGH (1) and
when switch is pressed (ON), the value at microcontroller will be LOW (0). The
program should be written to monitor the status of pin 0 (Port 7) to detect the
switch position (OFF/ON)

5. Key Debouncing Delay
• Generally bouncing and debouncing delay is
required to avoid wrong key detection in case of
momentary spike because of noise.
• This delay can be of 5ms to 10ms, which can be
implemented using timers.

6. 4x4 Matrix Keypad
• To increase the number of key connection,
keys can be connected in matrix. We will be able
to connect 16 keys using 4x4 matrix on one
microcontroller port (8 pins). Let's consider we
port 0 for key connection. First 4 pins from left
(X1, X2, X3, X4) are considered as row and rest 4
(Y1, Y2, Y3, Y4) are columns.
• We need to make rows pins (X1, X2, X3, X4) as
output pins and columns pins as input pints (Y1,
Y2, Y3, Y4). To make the pins as output, we load
the value LOW (0) to the pins. To configure pins as
input we make the pin HIGH(1). For example, if
key 1 is pressed then Y1 should goes LOW (0), as
X1 is low. X1 value is transferred to Y1. Similarly, it
will be applied for the rest of the keys as well.

7. 4x4 Matrix Keypad
• To configure X1, X2, X3, X4 as output, we
configured pins as LOW (0).
• To detect the switch position (pressed/released),
We need to make the Y1, Y2, Y3 and Y4 as high or
1.
• Otherwise, we will not be able to detect the
changes, of switch position (pressed/released)
• PORTX = 0xF0;

8. 4x4 Matrix Keypad
• Key2 Pressed: As key2 comes in X1 line make the X1 as LOW (0)
• X1 = 0; X2 = 1; X2 = 1; X4 = 1;
• Now if Y2 == 0 then considered that key2 is being pressed.
• Here _delay_ms(100) is deboucing delay to confirm the key pressed.
• X1 is for key1, key2, key3, key4 (scan from Y1, Y2, Y3, Y4 to detect key
pressed)
• X2 is for key5, key6, key7, key8(scan from Y1, Y2, Y3, Y4 to detect key
pressed)
• X3 is for key9, key10, key11, key12(scan from Y1, Y2, Y3, Y4 to detect key
pressed)
• X4 is for key13, key14, key15, key16(scan from Y1, Y2, Y3, Y4 to detect
key pressed)

9. PWM Output
PWM : Pulse Width Modulation
PWM is based on duty cycle variation which will
control the on & off time. It is being used for
multiple application.
Duty cycle = ON Time / Total Time
Example:
Total Time : 100ms
ON Time : 23ms
Duty Cycle : 23%
Duty cycle can be controlled based on timer
implementation to make the pin HIGH (1) and LOW
(0).
In most cases based on the certain Input signal
values, duty cycle will be decided.

10. LED Matrix
Depending on Interfacing type, HIGH or LOW will be sent on the port pin to make
the LED Glow.
/* To blink */
P0_0 = 1; /* Turn ON */
Delay_ms(100);
P0_0 = 0; /* Turn OFF */
Delay_ms(100);

11. LED Matrix
• Just like key Matrix we have LED matrix to
increase the number of connected LEDs. The
similary apporoach is being used here for LED
Matrix as well.
• To turn the specific LED ON, We need to set the
corresponding row pin to HIGH (1) and the column
pin to LOW (0)

12. LED Matrix
• const char raw[3] = {3,4,5};
• const char col[3] = {8,9,10};
• for (num =0; num<3; num++)
• {
• pinMode(raw[num]) = OUTPUT;
• pinMode(col[num]) = OUTPUT;
• digitalWrite(col[num]) = HIGH;
• }

13. LED Matrix
• void led_ON(int row, int col)
{
digitalWrite(pins_rows[row], HIGH);
digitalWrite(pins_cols[col], LOW);
}
void led_OFF(int row, int col)
{
digitalWrite(pins_rows[row], LOW);
digitalWrite(pins_cols[col], LOW);
}

14. ADC (Analog to Digital Convertors)
We always use analog to digital convertor to
measure the different parameters like
temperature, sound, pressure, light, voltage,
current etc. We will be able to store the recorded
values in controller or in memory as needed. We
need sensor which will gives us the analog values
corrosponding to the parameter which we are
going to measure. The output of sensor may be
linear or nonlinear depending on the type of
sensor. In case of linear output, it will be easy to
implement, process & map the values. However,
in case of nonlinear we may need to use table
which will be generally given in datasheet.

15. ADC (Analog to Digital Convertors)
• Analog to Digital Converter, commonly known as (ADC) is an electronic integrated circuit which is used to
convert the analog signals to digital form consisting of 1s/0s.Most of the ADCs take a voltage input as 0 to 5V,
etc. correspondingly ADC will produce digital output depending on the resolution of the ADC.
ADC can be based on I2C or SPI protocol, which is now commonly used across different industries.
• Serial ADC (SPI or I2C based ADC)
• Parallel ADC

16. ADC (Analog to Digital Convertors)

17. Output

18. Example:
Resolution
How to calculate voltage
corrosponding to 1 ADC
Count
10 bits ADC : 2^10 States :
1024 Values (5V)
• 0V = 0 ADC Count
• 5V = 1024 ADC Count
5000 mv/4095 = 1.23 mv
minimum change is
required to move 1 ADC
count
12 bits ADC : 2^12 States :
4096 Values (5V)
• 0V = 0 ADC Count
• 5V = 4095 ADC Count
5000 mv/1024 = 4.9 mv
minimum change is
required to move 1 ADC
count

19. Output

20. ADC Comparison

21. Alphanumeric
LCDs (16x2)

22. Alphanumeric LCDs
(16x2)

23. Alphanumeric
LCDs (16x2)
• The 16x2 Alphanumeric LCD means, I can show
up-to 2 lines of 16 characters. Each LCD character
contains the 5x8 pixel grid. The most LCD will have
two registers.
• Command Register (Required to send the
different
commands/instruction/operations)
• Data Register (Required to send data
to display on LCD)
• The LCD have the different required commands to
provide the display functionality.
Examples:
• Clear Display, shift display right, shift display left,
force cursor position at beginning of line1/line2
• Shift entire display right, Shift entire display left

24. Alphanumeric LCDs
(16x2)
• Address range of each lines:
• Line 1: 0x80
• Line 2: 0xC0
• The value of data register will be displayed on LCD. To display the value on LCD, we need to load
the ASCII value of characters in data register.

25. Alphanumeric
LCDs (16x2)
• Data Bus:
• Data bus contains the data lines from D0-D7. In 8-bit data bus mode, we can send the
data/command to LCD in bytes. Most LCD supports 4-bit mode where we can send the
data/command in chunks of 4-bit, which is used when we have limited available GPIO
lines on the microcontroller.
Register Select(RS): As we know LCD has two register namely
• Data register : To display data on the LCD, we should
write to the data register.
• To select between the command or the data register, the RS signal is used. If we make
the RS pin HIGH & feed input to the data lines (DB0 to DB7), this input will be interpreted
as the data that is to be displayed on the LCD screen.
• If the RS signal is HIGH, then the LCD interprets the 8-bit info (DB0 to DB7) as data and
copies it to data register. After that the LCD decodes the data for generating the 5x7
pattern and finally displays on the LCD.
• Command register : To send the different command to LCD, we should write
to command register.
• If we make the RS pin LOW and feed input to the data lines (DB0 to DB7), then this
will be interpreted as a command.
• If the RS signal is LOW, then the LCD interprets the 8-bit info (DB0 to DB7)
as Command and writes it Command register and performs the action as per the
command.

26. Alphanumeric
LCDs (16x2)
R/W (bar): Read / Write (bar)
• It is used switch between read & write operation mode.
• R/W (bar) = LOW (0), Indicates Write Mode
• R/W (bar) = HIGH (1), Indicates Read Mode
• This signal is used to write the data/command to LCD & reads
the busy flag of LCD. For write operation the RW should
be LOW and for read operation the R/W should be HIGH.
EN: Enable
• The Enable signal is used to latch the data (that is to place the
data on the data bus from D0 – D7 and wait for a clock or pulse to
send it), and when high to low pulse is sent into the E pin of LCD
the data is displayed on the LCD.
• A HIGH-to-LOW pulse is required be sent on enable pin, which
will latch the info into the LCD register. This will trigger the LCD to
act accordingly.

27. Alphanumeri
c LCDs

28. Alphanumeri
c LCDs

29. Alphanumeric
LCDs
Data send

30. Alphanumeric LCDs
Command Send

31. Alphanumeric
LCDs
Sequence:
• Send the command on data lines (DB0 to DB7)
• Select the command register using RS (RS = LOW)
• Select the write operation using R/W (bar), (RW = LOW)
• Send High to Low pulse on Enabler (EN) pin with delay

32. Alphanumeric
LCDs
Sequence:
• Send the ASCII data (Characters) required to displayed on-data lines
(DB0 to DB7)
• Select the data register using RS (RS = HIGH)
• Select the write operation using R/W (bar), (RW = LOW)
• Send High to Low pulse on Enabler (EN) pin with delay

33. Seven Segment Displays

34. Seven
Segment
Displays

35. Seven
Segment
Displays

36. Seven
Segment
Displays

37. Seven Segment
Displays
Digit gfedcba abcdefg a b c d e f g
0 0×3F 0×7E on on on on on on off
1 0×06 0×30 off on on off off off off
2 0×5B 0×6D on on off on on off on
3 0×4F 0×79 on on on on off off on
4 0×66 0×33 off on on off off on on
5 0×6D 0×5B on off on on off on on
6 0×7D 0×5F on off on on on on on
7 0×07 0×70 on on on off off off off
8 0×7F 0×7F on on on on on on on
9 0×6F 0×7B on on on on off on on
A 0×77 0×77 on on on off on on on
B 0×7C 0×1F off off on on on on on
C 0×39 0×4E on off off on on on off
D 0×5E 0×3D off on on on on off on
E 0×79 0×4F on off off on on on on
F 0×71 0×47 on off off off on on on

38. Seven
Segment
Displays

39. Interfacing
Memory

40. Interfacing
Memory
• START CONDITION: A high-to-low transition of SDA with SCL high is a
start condition which must precede any other command (refer to Start
and Stop Definition timing diagram).
• STOP CONDITION: A low-to-high transition of SDA with SCL high is a
stop condition. After a read sequence, the stop command will place the
EEPROM in a standby power mode (refer to Start and Stop Definition
timing diagram)

41. Interfacing
Memory

42. Interfacing
Memory

43. Interfacing
EEPROM

44. Interfacing
EEPROM

45. RS232 Vs RS485

46. RS232 Vs RS485
Description RS-232 RS-485
Transfer type Full duplex
Half duplex (2 wires),
full duplex (4 wires)
Maximum distance 15 meters at 9600 bps 1200 meters at 9600 bps
Contacts in use
TxD, RxD, RTS, CTS, DTR,
DSR, DCD, GND*
DataA, DataB, GND
Topology Point-to-Point Multi-point
Max. Number of connected
devices
1
32 (with repeaters larger, usually
up to 256)
Voltage Range
3V to 25V (Logic 0)
-3V to -25V (Logic 1)
200mV (Logic 0)
-200mV (Logic 1)

47. RS232 Vs
RS485

48. Questions