Introduction to the LCD1602 Liquid Crystal Display Module

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1. Product Overview

The LCD1602 character liquid crystal display module is specifically designed for displaying letters, numbers, symbols, etc. It supports 4-bit and 8-bit data transmission modes. It offers a 5×7 dot matrix display mode with a cursor. It provides a display data buffer DDRAM, character generator CGROM, and character generator CGRAM, allowing for the storage of up to 8 custom 5×8 dot matrix graphic character patterns in CGRAM. It features a rich set of command settings: clear display; cursor return to origin; display on/off; cursor on/off; character blinking; cursor shifting; display shifting, etc. It includes an internal power-on automatic reset circuit, which initializes the module when the external power supply voltage exceeds +4.5V, setting the module to its default display working state.

Pin Definitions:

VSS: Ground

VDD: Power +5V

VO: Liquid crystal display bias, connect to potentiometer VO

RS: Data/command selection

RW: Read/write selection

E: Enable signal for data transmission

D0-D3: Data, not used yet

D4-D7: Data, connected to GPIO

A: Positive terminal of backlight, connect to power +5V

S: Negative terminal of backlight, connect to ground

2. Technical Parameters

Display capacity: 16×2 characters

Chip operating voltage: 4.5—5.5V

Operating current: 2.0mA (5.0V)

Optimal operating voltage of the module: 5.0V

Character size: 2.95×4.35 (W×H) mm

3. Software Interface

LCD1602() – Create LCD1602 driver object

Function prototype:

lcd1602Obj = LCD1602(RS, RW, E, D4, D5, D6, D7)

Parameter description:

Parameter	Type	Required?	Description
RS	GPIO	Yes	Pass in GPIO object
RW	GPIO	Yes	Pass in GPIO object
E	GPIO	Yes	Pass in GPIO object
D4	GPIO	Yes	Pass in GPIO object
D5	GPIO	Yes	Pass in GPIO object
D6	GPIO	Yes	Pass in GPIO object
D7	GPIO	Yes	Pass in GPIO object

Return value: If successful, returns the LCD1602 object; if creation fails, throws an Exception

Example code:

from machine import Pin
import lcd1602

# Initialize the GPIO pins for the LCD
print('GPIO init begin')
# According to the configuration parameters of the device node named "RS" in board.json, and so on
gpioRSObj = Pin(2,Pin.OUT)
gpioRWObj = Pin(4,Pin.OUT)
gpioEObj = Pin(16,Pin.OUT)
gpioD4Obj = Pin(17,Pin.OUT)
gpioD5Obj = Pin(18,Pin.OUT)
gpioD6Obj = Pin(19,Pin.OUT)
gpioD7Obj = Pin(21,Pin.OUT)

print('GPIO init done')

lcd1602Obj = lcd1602.LCD1602(gpioRSObj, gpioRWObj, gpioEObj, gpioD5Obj, gpioD5Obj, gpioD5Obj, gpioD5Obj)
print('LCD inited!')

Output:

GPIO init begin
GPIO init done
LCD inited!

displayString(row, col, text) – Print characters to the specified row and column of the LCD screen

Functionality: Sets the cursor to the specified row and column offset position, then prints the character, where the row and column offset refers to the character offset rather than the dot matrix offset, with 2 rows and 16 columns

Function prototype:

drv.displayString(1, 0, ‘Hello’)

Parameter description:

row indicates the row offset, ranging from 0-1 indicating row 1-row 2

col indicates the column offset, ranging from 0-15 indicating column 1-column 16

text is the string to be printed

Return value: Number of characters printed successfully

Example:

# Print character Hello at row 2, column 1
from machine import Pin
import lcd1602

# Initialize the GPIO pins for the LCD
print('GPIO init begin')
# According to the configuration parameters of the device node named "RS" in board.json, and so on
gpioRSObj = Pin(2,Pin.OUT)
gpioRWObj = Pin(4,Pin.OUT)
gpioEObj = Pin(16,Pin.OUT)
gpioD4Obj = Pin(17,Pin.OUT)
gpioD5Obj = Pin(18,Pin.OUT)
gpioD6Obj = Pin(19,Pin.OUT)
gpioD7Obj = Pin(21,Pin.OUT)

print('GPIO init done')

lcd1602Obj = lcd1602.LCD1602(gpioRSObj, gpioRWObj, gpioEObj, gpioD5Obj, gpioD5Obj, gpioD5Obj, gpioD5Obj)
print('LCD inited!')
lcd1602Obj.displayString(1, 0, 'Hello')
print('LCD printed')

Output:

GPIO init begin
GPIO init done
LCD inited!
LCD printed

4. Interface Examples

Code:

# Python code
from machine import Pin
import lcd1602

if __name__ == '__main__':
    # Initialize the GPIO pins for the LCD
print('GPIO init begin')
# According to the configuration parameters of the device node named "RS" in board.json, and so on
gpioRSObj = Pin(2,Pin.OUT)
gpioRWObj = Pin(4,Pin.OUT)
gpioEObj = Pin(16,Pin.OUT)
gpioD4Obj = Pin(17,Pin.OUT)
gpioD5Obj = Pin(18,Pin.OUT)
gpioD6Obj = Pin(19,Pin.OUT)
gpioD7Obj = Pin(21,Pin.OUT)

print('GPIO init done')

lcd1602Obj = lcd1602.LCD1602(gpioRSObj, gpioRWObj, gpioEObj, gpioD5Obj, gpioD5Obj, gpioD5Obj, gpioD5Obj)
print('LCD inited!')
lcd1602Obj.displayString(1, 0, 'Hello')
print('LCD printed')

Output:

...
GPIO init begin
GPIO init done
LCD inited!
LCD printed
...

5. Communication Protocol

The communication between the main control chip and the LCD1602 controller is via GPIO communication, divided into initialization and command communication phases.

Initialization phase

Send 0x03 three times to initiate initialization requests to the LCD controller, with different intervals;

Immediately set the data/command transmission mode to 4 bits after initialization;

Then set the function, display mode, and print item mode, all via command communication;

Command communication phase

Select the instruction register of the LCD controller by setting RS=0, then send command content via D4-D7, enabling functions such as: clear display; cursor return to origin; display on/off; cursor on/off; character blinking; cursor shifting; display shifting, etc.

Select the data register of the LCD controller by setting RS=1, then send data content via D4-D7, enabling the function to print characters to the LCD screen;

4-wire transmission mechanism

Each command and data transmission is 8 bits, thus divided into two transmissions, each transmitting 4 bits

Transmission timing:

RS=0/1 first stabilizes the register display selection
Since we are only using write operations, RW=0 is kept low
Then prepare data on the D4-D7 pins, ready to notify the LCD to read
Control the E pin to generate a falling edge, where the high level needs to be maintained for >450ns
Since the LCD controller needs to read data and execute commands on the falling edge, maintain a stable time for command execution, which is 40us

6. Working Principle

The liquid crystal display screen has 16 pins drawn from the LCD controller for controlling command/data input via GPIO.

VSS is the ground power

VDD connects to the +5V power supply

VO is the contrast adjustment terminal of the liquid crystal display, connecting to the positive power supply gives the weakest contrast, while grounding gives the highest contrast. If the contrast is too high, it may cause a “ghosting” effect, which can be adjusted using a 10k ohm potentiometer.

RS is the register selection pin; a high level selects the data register, while a low level selects the instruction register.
RW is the read/write signal line; a high level indicates a read operation, while a low level indicates a write operation. When both RS and RW are low, commands or display addresses can be written; when RS is low and RW is high, busy signals can be read; when RS is high and RW is low, data can be written.
The E terminal is the enable terminal; when the E terminal transitions from high to low, the liquid crystal module reads the D0-D7 data and executes the command.
D0-D7 are 8-bit bidirectional data lines.
A is the positive terminal of the backlight.
K is the negative terminal of the backlight.