How to use GLCD display with Teensy or other MCU

 

On this topic I wrote an article [1] in 2015, where I modified the KS0108 library to apply it to the Teensy 3.1 board.

Now a simpler solution can be realized using the latest versions of the u8g2 library by Olikraus.

This article refers to the Teensy 3.1 MCU but it can be adapted to other MCUs, such as STM32 or others, simply by inserting the available pins in the library declaration, this graphic display requires 8 bits for the data bus and 5 for control.

The GLCD display I used is the ‘J’ version of the Winstar WG12864A, which only two more pins to obtain an RGB backlight with two more LEDs. This display has NT7108- NT7107 graphic controllers completely similar to the KS0108- KS0107. They have 64 channels: for a 128x64 pixel display you need two NT7108 chips for the 128 columns and an NT7107 for the 64 rows. Usually these chips are soldered on the pcb without a case and are covered with black resin, so we cannot read any sigle.

The advantages of using these displays are that they can be read even under the sun, excellent readability, good speed and relatively low consumption, the main disadvantage is that they require many output pins having an 8-bit parallel bus.

Although it is powered by 5 volts, it can also be connected to an MCU with 3.3 V levels, in fact all the signals are output and the R/W is always set to zero, as is done with alphanumeric LCDs.

The following table shows the connections with Teensy 3.1.

Pin	name	description	Teensy
1	VSS	Ground	Gnd
2	VDD	Supply voltage for logic	5V
3	Vo	LCD contrast (Pot. Cursor)	-
4	D/I	H: Data ,  L : Instruction (=DC)	9
5	R/W	Read/Write	4
6	E	Enable signal	17
7	DB0	Data bus line	2
8	DB1	Data bus line	14 /A0
9	DB2	Data bus line	7
10	DB3	Data bus line	8
11	DB4	Data bus line	6
12	DB5	Data bus line	20 /A6
13	DB6	Data bus line	21 /A7
14	DB7	Data bus line	5
15	CS1	Select Column 1~ Column 64	19
16	CS2	Select Column 65~ Column 128	18
17	/RES	Reset signal	23
18	Vout	Negative Voltage output	-
19	A	Anode LED backlight ( + )	-
20	KR	Cathode Red led	-
21	KG	Cathode Green led	-
22	KB	Cathode Blue led	-

Now I use the u8g2 library with the ability to use pins arbitrarily, in my case I configured:

U8G2_KS0108_128X64_F u8g2(U8G2_R0,2,14,7,8,6,20,21,5, /*E=*/17, /*dc=*/9, /*cs0=*/ 19, /*cs1=*/18, /*cs2=*/ U8X8_PIN_NONE, /*Res=*/23);

 

I chose the ‘Full buffer’ mode because it is faster and there are no memory problems with this MCU.

The parameters passed are: D0 - D7, E, D/I, CS1,CS2,none,Reset.

From tests I have done I understood that: cs0, is CS1 and cs1 = CS2 while cs2 does not exist for this display as each CS enables a chip that drives 64 channels and that, together with an NT7107 chip, creates a 64x64 pixel matrix that requires a memory of 512 bytes.

The library, after having configured it correctly, worked well. Of course, if you could transfer one byte at a time it would be faster, but the MCU is much faster than Arduino Uno and this is not a problem.

In the introductory photo you can see the example program “GraphicsTest.ino”.

To test the system I wrote this simple program:

/* TeensyGLCD program - I/O Teensy 3.1

uses a Winstar WG12864A Rev.J GLCD display

G. Carrrera 05/04/25*/

 

#include <U8g2lib.h>

U8G2_KS0108_128X64_F u8g2(U8G2_R0,2,14,7,8,6,20,21,5, /*E=*/17, /*dc=*/9, /*cs0=*/ 19, /*cs1=*/18, /*cs2=*/ U8X8_PIN_NONE, /*Res=*/23);

#define LCD_RW 4

void setup() {

  pinMode(LCD_RW, OUTPUT);

  digitalWrite(LCD_RW, LOW);  // Set R/W to low

  u8g2.begin();

  u8g2.clearBuffer(); // clear the internal memory

  //u8g2.setFont(u8g2_font_t0_11_tr);

  u8g2.setFont(u8g2_font_ncenB08_tr); // choose a suitable font

  u8g2.drawStr(0,10,"Teensy ADC to GLCD");

  u8g2.drawStr(0,20,"G.Carrrera 05/04/25");

  u8g2.sendBuffer();// transfer internal memory to the display

  delay(3000);  

}

 

void loop() {

 uint16_t ain = analogRead(22);// read analog input A8

 u8g2.clearBuffer();

 u8g2.setCursor(40, 40);

 u8g2.print("AD8= " + String(ain));

 u8g2.sendBuffer();

 delay(1000);

}

As you can see, the R/W signal must always be put on write, i.e. to ground. But in the circuit I made it was connected to pin 4, so I did it via software.

The diagram of my system can be found in the article cited.

 

References

1.       “A 128x64 GLCD for Teensy 3.x”, Giovanni Carrera, ArduPicLab 21/08/2015.

2.       https://github.com/olikraus/u8g2/wiki/u8g2reference