spec

1. Summary

The J204A is an industrial-grade character LCD module. It can display 4 lines of 20 characters each (80 characters in total).

2. Module Dimensions

3. Pin Interface Specifications

Pin Symbol Description Pin Symbol Description
1 VSS Ground (0V) 9 D2 Data Bit 2
2 VDD Power Supply (+5V) 10 D3 Data Bit 3
3 VL Contrast Adjustment (Bias) 11 D4 Data Bit 4
4 RS Register Select (Data/Command) 12 D5 Data Bit 5
5 R/W Read/Write Select 13 D6 Data Bit 6
6 E Enable Signal 14 D7 Data Bit 7
7 D0 Data Bit 0 15 BLA Backlight Positive (+5V)
8 D1 Data Bit 1 16 BLK Backlight Negative (0V)

Pin Details:

  • Pin 1 (VSS): System Ground.
  • Pin 2 (VDD): +5V Power Supply.
  • Pin 3 (VL): LCD contrast adjustment. Connecting it to VDD provides the lowest contrast, while GND provides the highest contrast. A 10K Ohm potentiometer is recommended to permit adjustment. "Ghosting" may occur if contrast is set too high.
  • Pin 4 (RS): Register Select. High level selects the Data Register; Low level selects the Instruction Register.
  • Pin 5 (R/W): Read/Write Select. High level for Read operations; Low level for Write operations.
    • When RS=Low, R/W=Low: Write Command/Instruction.
    • When RS=Low, R/W=High: Read Busy Flag and Address Counter.
    • When RS=High, R/W=Low: Write Data.
    • When RS=High, R/W=High: Read Data.
  • Pin 6 (E): Enable signal. A transition from High to Low (falling edge) triggers the LCD module to execute the instruction.
  • Pins 7 to 14 (D0-D7): 8-bit bidirectional data bus.
  • Pin 15 (BLA): Backlight Anode (+).
  • Pin 16 (BLK): Backlight Cathode (-).

4. Control Instructions

The J204A LCD module uses an internal controller with 11 standard instructions:

No. Instruction RS R/W D7 D6 D5 D4 D3 D2 D1 D0
1 Clear Display 0 0 0 0 0 0 0 0 0 1
2 Return Home 0 0 0 0 0 0 0 0 1 *
3 Entry Mode Set 0 0 0 0 0 0 0 1 I/D S
4 Display On/Off 0 0 0 0 0 0 1 D C B
5 Cursor/Display Shift 0 0 0 0 0 1 S/C R/L * *
6 Function Set 0 0 0 0 1 DL N F * *
7 Set CGRAM Address 0 0 0 1 A A A A A A
8 Set DDRAM Address 0 0 1 A A A A A A A
9 Read Busy Flag 0 1 BF A A A A A A A
10 Write Data 1 0 D D D D D D D D
11 Read Data 1 1 D D D D D D D D

Note: A = Address bit, D = Data bit, * = Don't care.

Instruction Details:

  1. Clear Display (01H): Clears the entire display and resets the cursor to address 00H.
  2. Return Home: Resets the cursor to address 00H without clearing the display.
  3. Entry Mode Set:
    • I/D: 1 = Increment (right), 0 = Decrement (left).
    • S: 1 = Shift display, 0 = No shift.
  4. Display On/Off:
    • D: 1 = Display On, 0 = Display Off.
    • C: 1 = Cursor On, 0 = Cursor Off.
    • B: 1 = Cursor Blinking, 0 = No Blinking.
  5. Cursor/Display Shift:
    • S/C: 1 = Display Shift, 0 = Cursor Move.
    • R/L: 1 = Shift Right, 0 = Shift Left.
  6. Function Set:
    • DL: 1 = 8-bit bus, 0 = 4-bit bus.
    • N: 1 = 2-line display (includes 4-line models), 0 = 1-line.
    • F: 1 = 5x10 dots, 0 = 5x7 dots.
  7. Set CGRAM Address: Sets the Character Generator RAM address.
  8. Set DDRAM Address: Sets the Display Data RAM address.
  9. Read Busy Flag (BF): BF=1 indicates the module is busy and cannot receive new commands.
  10. Write Data: Writes data content to RAM.
  11. Read Data: Reads data content from RAM.

5. Timing Sequences

Read Operation Sequence

Write Operation Sequence

6. RAM Address Mapping

The LCD is a slow device. Before sending any instruction, ensure the Busy Flag (BF) is Low (0). To display a character, you must first specify the DDRAM address.

Internal Display Addresses (Hex)

The J204A spans 4 lines. For example, the first character of the second line is at address 40H. To set the cursor to this position, the command must include the high bit (D7=1).

  • Internal Address: 40H (Binary: 01000000)
  • Command Calculation: 40H + 80H = C0H (Binary: 11000000)

During initialization, the display mode should be set. Usually, characters are entered with the cursor automatically moving to the right.

char table

7. C51 Example Code

#include <reg52.h>

#define uint  unsigned int
#define uchar unsigned char

#define comm 0
#define dat  1

sbit rs = P3^5; // Register Select: H=Data, L=Command
sbit rw = P3^4; // Read/Write: H=Read, L=Write
sbit e  = P3^3; // Enable signal

uchar code tab1[] = "Electrodragon.com TEL: 18576608994";

void delay(uint ms) {
    uint i, j;
    for(i = 0; i < ms; i++) {
        for(j = 0; j < 120; j++);
    }
}

void wr_lcd(uchar type, uchar content) {
    if(type == dat) {
        rs = 1; // Data
        rw = 0; // Write
    } else {
        rs = 0; // Command
        rw = 0; // Write
    }
    P1 = content;
    e = 1;
    delay(1);
    e = 0;
}

void init_lcd(void) {
    e = 0;
    wr_lcd(comm, 0x38); // 8-bit interface, 2-line mode (works for 4-line)
    wr_lcd(comm, 0x01); // Clear screen
    wr_lcd(comm, 0x06); // Cursor move direction (increment)
    wr_lcd(comm, 0x0c); // Display On, Cursor Off
}

void chrt_disp(uchar code *chrt) {
    uchar i, j;
    wr_lcd(comm, 0x80); // Set DDRAM address to 00H
    for(j = 0; j < 2; j++) {
        for(i = 0; i < 16; i++) {
            wr_lcd(dat, chrt[j * 16 + i]);
        }
        wr_lcd(comm, 0xc0); // Move to second line (40H)
    }
}

void cgram_wr(uchar zm_data1, uchar zm_data2) {
    uchar i, j;
    wr_lcd(comm, 0x40); // Set CGRAM address 00H
    for(j = 0; j < 8; j++) {
        for(i = 0; i < 4; i++) {
            wr_lcd(dat, zm_data1);
            wr_lcd(dat, zm_data2);
        }
    }
}

void cgram_disp(void) {
    uchar i, j;
    wr_lcd(comm, 0x80);
    for(j = 0; j < 2; j++) {
        for(i = 0; i < 8; i++) {
            wr_lcd(dat, i);
        }
        wr_lcd(comm, 0xc0);
    }
}

void main(void) {
    init_lcd();
    while (1) {
        chrt_disp(tab1);
        delay(2000);
        
        cgram_wr(0x1f, 0x1f); 
        cgram_disp(); 
        delay(2000);
        
        cgram_wr(0x15, 0x15);
        cgram_disp(); 
        delay(2000);
        
        cgram_wr(0x1f, 0x00);
        cgram_disp();
        delay(2000);
        
        cgram_wr(0x15, 0x0a);
        cgram_disp(); 
        delay(2000);
    }
}

ref

datasheet == Tech-dat/interactive-dat/display-dat/LCD-dat/LCD2004-dat/2004A-DS.pdf

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https://www.electrodragon.com