3-Wire Serial LCD using PIC12F683


Posted on Jul 11, 2012

The character data and command from the microcontroller is transferred serially to a shift register (74HC595), and the parallel output from the shift register is fed to LCD pins. 74HC595 is a high-speed 8-bit serial in, serial or parallel-out shift register with a storage register and 3-state outputs. The shift register and storage registers have separate clocks, SH_CP and ST_CP respectively. Data in the shift register is shifted on the positive-going transitions of SH_CP, and the content of shift register will be transferred to the storage register on a positive-going transition of the ST_CP. If we tie both the clocks together, the shift register will always be one clock ahead of the storage register. The 8-bit data of the storage register will appear at the parallel output (Q0-Q7) when the output enable (OE) is low.


3-Wire Serial LCD using PIC12F683
Click here to download the full size of the above Circuit.

In this project, SH_CP and ST_CP are tied together. So, if we want to receive a serially transferred 8-bit into parallel form at Q0-Q7, an extra clock pulse is required after transmitting the 8-th bit of serial data because the clocks are tied and the storage register is 1-clock behind the shift register. The hardware part of this project is fairly simple. The challenging part is to write the driver software that is responsible for a proper sequence of operations required to serially transfer character data and command to 74HC595 serial-in parallel-out shift register. The shift register parallel output is then connected to LCD data lines (D4-D7) and RS control pin. This arrangement requires 3-pins of microcontroller to display character data on a parallel LCD display: 2 pins for providing Clock and Data to 74HC595, and 1 pin for enable control (E) pin of LCD module. Since the data transfer uses 4-bit mode, any 8-bit command or character data is sent in two steps: send the higher nibble first, and then the lower nibble. The R/W control pin is grounded, and therefore no data or status read from the LCD module is possible in this case. A first, a bit of data fed to DS pin of 74HC595 appears at Q0 output after 2 clocks (because SH_CP and ST_CP are tied). So, sending 4-bit data (D4-D7) and an RS signal require 6 clock pulses till they appear at Q0-Q4 outputs respectively. When the LCD module is turned ON, it is initialized in...




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Door Chime with ATtiny12
Analogue / Digital Logger II
Receiver monitor
12V Car Battery Charger
Simple Analog Multiplier Circuit Using LM107
DS1621 IIC interface under Linux drives designing
Making The LCD Expansion Board for PIC18F4520
Menci alarm produced schematic circuit diagram
22kW and below hoist with Y- transfer power-saving circuit



Top