What is Latche?
what is latch? A latch is a flip flop or combination of flip flops that can store data bits in it. A single flip flop can store a single bit information at a time. Latches are used to build sequential circuits. The latch which i am using in this tutorial is 74ls574. It is an 8-bit latch, which means it can store 8-bit information at a time. It has 20 pins. One vcc apply +5v to it. GND make it ground. 8 input-pins and 8 output-pins. Two most important pins of the latches are OE and CP.
- CP- CP is clock Pulse. When CP is supplied with Low to High pulse (L-H) then the data on the input pins are stored in the internal flip flops of the latch.
- OE- OE is enable latch. When OE is made ‘0’ data stored in the flip flops appeared on the output pins. When its 1 nothing will appear on the output its void or GND.
I used 74ls574 because of its simple one direction input and one direction output. The pic below clearly clears the concept.
What the project is doing?
8051 Latch interface – Project Circuit
Microcontroller used in the Project is 89c52 microcontroller. 11.0592 MHz crystal is used in the project to generate clock pulses for microcontroller operation. 40×4 character lcd is interfaced in 8-bit mode with 89c51 microcontroller. Data pins of Lcd are connected to Port-1 of 89c52. Lcd controlling pins RS(Register-Select) is connected to Port-3 Pin#2. RW(Read-Write) is connected to Port-3 Pin#0. Enable for first HD44780 lcd controller is connected to Port-3 Pin#1. Enable for second HD44780 lcd controller is connected to Port-3 Pin#3.
Latches are enabled using Port-2. Port-2 Pin#4 enables first latch Pin#5 second Pin#6 third and Pin#7 fourth. All the latches are connected to Common Clock. CP is provided using Port-2 Pin#3.
Project working principle
For high input(1) at latch an upward arrow will be displayed on lcd for that particular input. For Low input(0) at latch a downward arrow will be displayed on lcd for that particular input. Upward and Downward arrows are generated in CG-RAM of lcd. They are not text so we first have to create them. I first created them in CG-RAM(Character Generated RAM) of lcd then i displayed them on lcd where needed.
- String displayed on Lcd first line is ” SMART PLC(Programable Logic Controler)“.
- String displayed on Lcd second line is 1st and 2nd Latch status (Upwards Downwards Arrows)
- String displayed on Lcd third line is 3rd and 4th Latch status (Upwards Downwards Arrows)
- String displayed on Lcd fourth line is “I/O Energized I/O Denergized“.