interface 16x2 LCD with 8051 microcontroller

Interface a keypad with Microcontroller

Keypad is a widely used input device with lots of application in our everyday life. From a simple telephone to keyboard of a computer, ATM, electronic lock, etc., keypad is used to take input from the user for further processing. In this article we are interfacing keypad with the MCU AT89C51 and displaying the corresponding number on LCD. This module can be further used in a number of systems to interfaced keypad with microcontroller and other processors to get desired output.

Keypad is organized as a matrix of switches in rows and column. The article uses a 4X3 matrix keypad and a 16x2 LCD for displaying the output of keypad.
The circuit diagram shows the connection of keypad with the controller. Port P2 of the microcontroller is used to send the data for displaying on the LCD. P1^1, P1^2, P1^3 pins of microcontroller is connected to RS, RW, EN pins of LCD respectively. Port P0 is used to scan input from the keypad (refer circuit diagram for connection).

The concept of interfacing keypad with the MCU is simple. Every number is assigned two unique parameters, i.e., row and column number (n(R, C) for example 6 (2, 3)). Hence every time a key is pressed the number is identified by detecting the row and column number of the key pressed.

Initially all the rows are set to zero by the controller and the columns are scanned to check if any key is pressed. In case no key is pressed the output of all the columns will be high.

Internal block diagram of DACO800

• The DAC0800 is an 8-bit, high speed, current output DAC with a typical settling time (conversion time) of 100 ns.

• It produces complementary current output, which can be converted to voltage by using simple resistor load.

• The DAC0800 require a positive and a negative supply voltage in the range of ± 5V to ±18V.

• It can be directly interfaced with TTL, CMOS, PMOS and other logic families.

• For TTL input, the threshold pin should be tied to ground (VLC = 0V).

• The reference voltage and the digital input will decide the analog output current, which can be converted to a voltage by simply connecting a resistor to output terminal or by using an op-amp I to V converter.

• The DAC0800 is available as a 16-pin IC in DIP

Interfacing of 4x4 matrix keyboard and 4 digit 7 segment display

• 4 scan lines are sufficient to scan matrix keyboard and to select display digits. Hence decoded mode is used.

Block diagram of ADC0809/ADC0808

Interfacing of 8255 with 8085 processor

INTERFACING OF 8X8 MATRIX KEYBOARD IN INTERRUPT KEYBORD MODE

Intel 8279 Keyboard/Display Controller

• The Intel 8279 is a Keyboard/Display Controller is specially developed for interfacing keyboard and display devices for the Intel 8085, 8086 and 8088 microprocessors

• Simultaneous keyboard and display operations

• Scanned keyboard mode.

• Scanned sensor mode.

• 8-character keyboard FIFO.

• Right or left entry 16-byte display RAM.

• Programmable scan timing.

PINOUT OF PIC 16F876

ARCHITECTURE OF PIC 16F876