Interfacing the Keyboard to 8051 Micro Controller 11

8/4/2019 Interfacing the Keyboard to 8051 Micro Controller 11

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Interfacing the Keyboard to 8051 microcontroller

The key board here we are interfacing is a matrix keyboard. This key board is designed with aparticular rows and columns. These rows and columns are connected to the microcontroller through its poof the micro controller 8051. We normally use 8*8 matrix key board. So only two ports of 8051 can be easconnected to the rows and columns of the key board.

When ever a key is pressed, a row and a column gets shorted through that pressed key and all other keys are left open. When a key is pressed only a bit in the port goes high. Which indicamicrocontroller that the key is pressed. By this high on the bit key in the corresponding column is identifie

Once we are sure that one of key in the key board is pressed next our aim is to identify that key. do this we firstly check for particular row and then we check the corresponding column the key board.

To check the row of the pressed key in the keyboard, one of the row is made high by making onebit in the output port of 8051 high . This is done until the row is found out. Once we get the row next outs to find out the column of the pressed key. The column is detected by contents in the input ports withhelp of a counter. The content of the input port is rotated with carry until the carry bit is set.

The contents of the counter is then compared and displayed in the display. This display is desigusing a seven segment display and a BCD to seven segment decoder IC 7447.

The BCD equivalent number of counter is sent through output part of 8051 displays the numbepressed key.

Circuit diagram of INTERFACING KEY BOARD TO 8051.

The programming algorithm, program and the circuit diagram is as follows. Here program is explained wcomments.



Circuit diagram of INTERFACING KEY BOARD TO 8051.

Keyboard is organized in a matrix of rows and columns as shown in the figure. The microcontroller accesses both rows and columns through the port.

1. The 8051 has 4 I/O ports P0 to P3 each with 8 I/O pins, P0.0 to P0.7,P1.0 to P1.7P2.0 to P2.7, P3.0 to P3.7. The one of the port P1 (it understood that P1 means P1.0 toP1.7) as an I/P port for microcontroller 8051, port P0 as an O/P port of microcontroller

8051 and port P2 is used for displaying the number of pressed key.2. Make all rows of port P0 high so that it gives high signal when key is pressed.3. See if any key is pressed by scanning the port P1 by checking all columns fornon zero condition.4. If any key is pressed, to identify which key is pressed make one row high at atime.5. Initiate a counter to hold the count so that each key is counted.6. Check port P1 for nonzero condition. If any nonzero number is there in[accumulator], start column scanning by following step 9.7. Otherwise make next row high in port P1.8. Add a count of 08h to the counter to move to the next row by repeating steps

from step 6.9. If any key pressed is found, the [accumulator] content is rotated right throughthe carry until carry bit sets, while doing this increment the count in the counter tillcarry is found.

10. Move the content in the counter to display in data field or to memory location

11. To repeat the procedures go to step 2.



BASICS OF STEPPER MOTOR

Of all motors, step motor is the easiest to control. It's handling simplicity is really hard to deny

- all there is to do is to bring the sequence of rectangle impulses to one input of step controller

and direction information to another input. Direction information is very simple and comes

down to "left" for logical one on that pin and "right" for logical zero. Motor control is also very

simple - every impulse makes the motor operating for one step and if there is no impulse the

motor won't start. Pause between impulses can be shorter or longer and it defines revolution

rate. The picture below represents the scheme for connecting the step motor to

microcontroller and appropriate program code follows.

The key to driving a stepper is realizing how the motor is constructed. A diagram shows the

representation of a 4 coil motor, so named because 4 coils are used to cause the revolution of

the drive shaft. Each coil must be energized in the correct order for the motor to spin.

In Figure boxes are used to represent switches; a control unit, not shown, is responsible for

providing the control signals to open and close the switches at the appropriate times in order

to spin the motors. The control unit is commonly a computer or programmable interface

controller, with software directly generating the outputs needed to control the switches.

Step angle

It is angle through which motor shaft rotates in one step. step angle is different for different

motor . selection of motor according to step angle depends on the application , simply if you

require small increments in rotation choose motor having smaller step angle.

No of steps require to rotate one complete rotation = 360 deg. / step angle in deg.

Steps/second

The relation between RPM and steps per sec. is given by ,

steps or impulses /sec. =(RPM X Steps /revolution ) /60

So referring to RPM value in datasheet you can calculate steps/sec and from it delay or

pause between impulses



INTERFACING TO 8051.

To cause the stepper to rotate, we have to send a pulse to each coil in turn. The 8051 does

not have sufficient drive capability on its output to drive each coil, so there are a number of

ways to drive a stepper,Stepper motors are usually controlled by transistor or driver IC .

Driving current for each coil is then needed about 60mA at +5V supply. A Darlington transistor

array, ULN2003 is used to increase driving capacity of the 8051 chip. Four 4.7k resistors help

the 8051 to provide more sourcing current from the +5V supply.

Stepping Sequence

Coil A Coil B Coil C Coil D Step

0 1 1 0 1

0 0 1 1 2

1 0 0 1 3

1 1 0 0 4



Analog to Digital Converter (ADC) Interfacing

ANALOG DIGITAL TO CONVERTER - ADC

Commonly used ADC device – ADC804

PinOut • CS – Chip Select , active low

• RD – Read Digital data from ADC, H-L edge triggered

• WR -- Start conversion, L-H pulse edge triggered

• INTR -- end of conversion, Goes low to indicate conversion done

• Data bits -- D0-D7

• CLK IN & CLK R

– CLK IN is an input pin connected to an external clock source when an external clock is used

for timing. However, ADC804 has an internal clock generator.

Data OutDout = Vin / Step Size

Conversion Time Greater than 110us for ADC804

Resolution 8 bits for ADC804

INTERFACING ADC804 TO 8051

Signals to be interfaced (on the ADC804)

– D0-D7, RD, WR, INTR, CSCan do both Memory mapping and IO mapping

Memory Mapping (timing is critical)– Connect D0-D7 of ADC804 to the data bus of the 8051 system– Connect RD, WR of the ADC804 to the 8051 system (ensure polarity)– Connect CS of ADC804 to an appropriate address decoder output– Connect INTR of ADC804 to an external interrupt Pin on the 8051 (INT0 or INT1)

IO Mapping

– Connect D0-D7, RD, WR, CS, INTR to some port bits on the 8051 (12 in all).

Algorithm• Make CS=0 and send a low-to-high to pin WR to start the conversion.

• Keep monitoring INTR

– If INTR =0, the conversion is finished and we can go to the next step.

– If INTR=1, keep polling until it goes low.

• After INTR=0, we make CS=0 and send a high-to-low pulse to RD to get the data out of the

ADC804 chip.



LCD interfacing

UNDERSTANDING LCD

Pinout

• 8 data pins D7:D0Bi-directional data/command pins.

Alphanumeric characters are sent in ASCII format.

• RS: Register Select

RS = 0 -> Command Register is selected

RS = 1 -> Data Register is selected

• R/W: Read or Write

0 -> Write, 1 -> Read

• E: Enable (Latch data)

Used to latch the data present on the data pins.

A high-to-low edge is needed to latch the data.

• VEE : contrast control

NOTE: When writing to the display, data is transferred only on the high to low transition of this

signal. However, when reading from the display, data will become available shortly after the

low to high transition and remain available until the signal falls low again.

Display Data RAM (DDRAM)

Display data RAM (DDRAM) is where you send the characters (ASCII code) you want to see on

the LCD screen. It stores display data represented in 8-bit character codes. Its capacity is 80

characters (bytes). Below you see DD RAM address layout of a 2*16 LCD.

Character Generator RAM (CGRAM)-User defined character RAM



In the character generator RAM, we can define our own character patterns by program. CG

RAM is 64 bytes ,allowing for eight 5*8 pixel, character patterns to be defined. However how

to define this and use it is out of scope of this tutorial. So I will not talk any more about

CGRAM

Registers

The LCD HD44780 has two 8-bit registers, an instruction register (IR) and a data register

(DR). The IR stores instruction codes. The DR temporarily stores data to be written into

DDRAM or CGRAM and temporarily stores data to be read from DDRAM or CGRAM. Data

written into the DR is automatically written into DDRAM or CGRAM by an internal operation. .

These two registers can be selected by the register selector (RS) signal. See the table below:

Register Selection

RS R/W Operation

0 0 IR write as an internal operation (display clear, etc.)

0 1 Read busy flag (DB7) and address counter (DB0 to DB6)

1 0 DR write as an internal operation (DR to DDRAM or CGRAM)

1 1 DR read as an internal operation (DDRAM or CGRAM to DR)

Busy Flag (BF)

When the busy flag is 1, the LCD is in the internal operation mode, and the next instructionwill not be accepted. When RS = 0 and R/W = 1 (see the table above), the busy flag is outputto DB7 (MSB of LCD data bus). The next instruction must be written after ensuring that thebusy flag is 0.

LCD Commands

The LCD’s internal controller accepts several commands and modifies the display accordingly.

These commands would be things like:

– Clear screen

– Return home

– Shift display right/left

Entry mode set

This command sets cursor move direction and display shift ON/OFF. There are 4 possible

function set commands;04, 05, 06, and 07. This command changes the direction the cursor

moves by setting the address counter to increment or decrement.

INTERFACING LCD TO 8051



The LCD requires 3 control lines as well as either 4 or 8 I/O lines for the data bus. The usermay select whether the LCD is to operate with a 4-bit data bus or an 8-bit data bus.

If a 4-bit data bus is used, the LCD will require a total of 7 data lines.If an 8-bit data bus is used, the LCD will require a total of 11 data lines.

The three control lines are EN, RS, and RW.

Note that the EN line must be raised/lowered before/after each instruction sent to the LCDregardless of whether that instruction is read or write, text or instruction. In short, you mustalways manipulate EN when communicating with the LCD. EN is the LCD's way of knowing thatyou are talking to it. If you don't raise/lower EN, the LCD doesn't know you're talking to it onthe other lines.

Checking the Busy Flag

You can use subroutine for checking busy flag or just a big (and safe) delay.

1. Set R/W Pin of the LCD HIGH(read from the LCD)2. Select the instruction register by setting RS pin LOW3. Enable the LCD by Setting the enable pin HIGH4. The most significant bit of the LCD data bus is the state of the busy

flag(1=Busy,0=ready to accept instructions/data). The other bits hold the currentvalue of the address counter.

If the LCD never come out from”busy" status because of some problems, The program will"hang," waiting for DB7 to go low



DAC INTERFACING

This section will show how to interface a DAC (digital-to-analog converter) to the 8051.

Digital-to-analog (DAC) converter

The digital-to-analog converter (DAC) is a device widely used to convert digital pulses to

analog signals. In this section we discuss the basics of interfacing a DAC to the 8051.Recall from your digital electronics book the two methods of creating a DAC: binary

weighted and R/2R ladder. The vast majority of integrated circuit DACs, including the

MC1408 (DAC0808) used in this section, use the R/2R method since it can achieve a

much higher degree of precision.. The number of data bit inputs decides the resolution of

the DAC since the number of analog output levels is equal to 2″, where n is the number of

data bit inputs. Therefore, an 8-input DAC such as the DAC0808 provides 256 discrete

voltage (or current) levels of output.

MC1408 DAC (or DAC0808)

In the MC1408 (DAC0808), the digital inputs are converted to current (Iout), and by

connecting a resistor to the Iout pin, we convert the result to voltage.

The total current provided by the Iout pin is a function of the binary numbers at the DO – D7

inputs of the DAC0808 and the reference current (Iref), and is as follows:

where DO is the LSB, D7 is the MSB for the inputs, and Iref is the input

Interfacing the Keyboard to 8051 Micro Controller 11

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