Hardware

It is essential that you get your device correctly wired to your single-board computer (SBC). The needed connections vary based upon the type of interface your device supports. There three major styles of interfaces that are popular with small LCD displays. These include I2C, SPI and 6800 style parallel-bus interfaces.

I2C vs. SPI vs Parallel

If you have not yet purchased your display, you may be wondering if you should get an I2C, SPI or parallel-bus display. The basic trade-off is implementation complexity and speed. The I2C is the easiest to connect because it has fewer pins while SPI may have a faster display update rate due to running at a higher frequency and having less overhead. Parallel-bus displays are both slower and harder to connect but are typically less expensive.

Identifying your interface

You can determine if you have an I2C, SPI or parallel-bus interface by counting the number of pins on your card. An I2C display will have 4 pins while an SPI interface will have 6 or 7 pins, and a parallel-bus interface will typically need to have at least 9 pins connected on a device but can requires 16 or more depending on the size of the bus and what other signals are required.

If you have a SPI display, check the back of your display for a configuration such as this:

serial config

For this display, the two 0 Ohm (jumper) resistors have been connected to “0” and the table shows that “0 0” is 4-wire SPI. That is the type of connection that is currently supported by the SPI mode of this library.

Tip

  • If you don’t want to solder directly on the Pi, get 2.54mm 40 pin female single row headers, cut them to length, push them onto the Pi pins, then solder wires to the headers.

  • If you need to remove existing pins to connect wires, be careful to heat each pin thoroughly, or circuit board traces may be broken.

  • Triple check your connections. In particular, do not reverse VCC and GND.

I2C

I2C interfaces are the simplest to wire as they contain the smallest number of pins. The only signal lines are serial data (SDA) and serial clock (SCL). That plus the power and ground connections complete the required connections.

If you are using a Raspberry Pi you will normally attach to header P1. The P1 header pins should be connected as follows:

Device Pin

Name

Remarks

RPi Pin

RPi Function

1

GND

Ground

P01-6

GND

2

VCC

+3.3V Power

P01-1

3V3

3

SCL

Clock

P01-5

GPIO 3 (SCL)

4

SDA

Data

P01-3

GPIO 2 (SDA)

See also

Alternatively, on rev.2 RPi’s, right next to the male pins of the P1 header, there is a bare P5 header which features I2C channel 0, although this doesn’t appear to be initially enabled and may be configured for use with the Camera module.

Device Pin

Name

Remarks

RPi Pin

RPi Function

Location

1

GND

Ground

P5-07

GND

_images/RPi_P5_header.png

2

VCC

+3.3V Power

P5-02

3V3

3

SCL

Clock

P5-04

GPIO 29 (SCL)

4

SDA

Data

P5-03

GPIO 28 (SDA)

Enabling The I2C Interface

The I2C interface may not be enabled by default on your SBC. To check if it is enabled:

$ dmesg | grep i2c
[    4.925554] bcm2708_i2c 20804000.i2c: BSC1 Controller at 0x20804000 (irq 79) (baudrate 100000)
[    4.929325] i2c /dev entries driver

or:

$ lsmod | grep i2c
i2c_dev                 5769  0
i2c_bcm2708             4943  0
regmap_i2c              1661  3 snd_soc_pcm512x,snd_soc_wm8804,snd_soc_core

If you have no kernel modules listed and nothing is showing using dmesg then this implies the kernel I2C driver is not loaded.

For the Raspberry PI running Raspbian, enable the I2C as follows:

  1. Run sudo raspi-config

  2. Use the down arrow to select 5 Interfacing Options

  3. Arrow down to P5 I2C

  4. Select yes when it asks you to enable I2C

  5. Also select yes when it asks about automatically loading the kernel module

  6. Use the right arrow to select the <Finish> button

After rebooting re-check that the dmesg | grep i2c command shows whether I2C driver is loaded before proceeding. You can also enable I2C manually if the raspi-config utility is not available.

Optionally, to improve performance, increase the I2C baudrate from the default of 100KHz to 400KHz by altering /boot/config.txt to include:

dtparam=i2c_arm=on,i2c_baudrate=400000

Then reboot.

Next, add your user to the i2c group and install i2c-tools:

$ sudo usermod -a -G i2c pi
$ sudo apt-get install i2c-tools

Logout and in again so that the group membership permissions take effect

Determining Address

Check that the device is communicating properly (if using a rev.1 board, use 0 for the bus, not 1) and determine its address using i2cdetect:

$ i2cdetect -y 1
       0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
  00:          -- -- -- -- -- -- -- -- -- -- -- -- --
  10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  30: -- -- -- -- -- -- -- -- -- -- -- -- 3c -- -- --
  40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
  70: -- -- -- -- -- -- -- --

The address for your device will be needed when you initialize the interface. In the example above, the display address is 0x3c. Keep in mind that I2C buses can have more than one device attached. If more than one address is shown when you run i2cdetect, you will need to determine which one is associated with your display. Typically displays will only support a limited set of possible addresses (often just one). Checking the documentation can help determine which device is which.

SPI

The GPIO pins used for this SPI connection are the same for all versions of the Raspberry Pi, up to and including the Raspberry Pi 4 B.

Warning

There appears to be varying pin-out configurations on different display modules! Make sure to verify the pin numbers of your device by their function especially VCC and GND.

Device Pin

Name

Remarks

RPi Pin

RPi Function

1

VCC

+3.3V Power

P01-17

3V3

2

GND

Ground

P01-20

GND

3

D0

Clock

P01-23

GPIO 11 (SCLK)

4

D1

MOSI

P01-19

GPIO 10 (MOSI)

5

RST

Reset

P01-22

GPIO 25

6

DC

Data/Command

P01-18

GPIO 24

7

CS

Chip Select

P01-24

GPIO 8 (CE0)

Note

  • If you’re already using the listed GPIO pins for Data/Command and/or Reset, you can select other pins and pass gpio_DC and/or gpio_RST argument specifying the new GPIO pin numbers in your serial interface create call (this applies to PCD8544, ST7567, ST7735 and ST7789).

  • Because CE is connected to CE0, the display is available on SPI port 0. You can connect it to CE1 to have it available on port 1. If so, pass port=1 in your serial interface create call.

  • When using the 4-wire SPI connection, Data/Command is an “out of band” signal that tells the controller if you’re sending commands or display data. This line is not a part of SPI and the library controls it with a separate GPIO pin. With 3-wire SPI and I2C, the Data/Command signal is sent “in band”.

  • If you’re already using the listed GPIO pins for Data/Command and/or Reset, you can select other pins and pass a gpio_DC and/or a gpio_RST argument specifying the new BCM pin numbers in your serial interface create call.

  • The use of the terms 4-wire and 3-wire SPI are a bit confusing because in most SPI documentation, the terms are used to describe the regular 4-wire configuration of SPI and a 3-wire mode where the input and output lines, MOSI and MISO, have been combined into a single line called SISO. However, in the context of these LCD controllers, 4-wire means MOSI + Data/Command and 3-wire means Data/Command sent as an extra bit over MOSI.

Enabling The SPI Interface

To enable the SPI port on a Raspberry Pi running Raspbian:

$ sudo raspi-config
> Advanced Options > A6 SPI

If raspi-config is not available, enabling the SPI port can be done manually.

Ensure that the SPI kernel driver is enabled:

$ ls -l /dev/spi*
crw-rw---- 1 root spi 153, 0 Nov 25 08:32 /dev/spidev0.0
crw-rw---- 1 root spi 153, 1 Nov 25 08:32 /dev/spidev0.1

or:

$ lsmod | grep spi
spi_bcm2835             6678  0

Then add your user to the spi and gpio groups:

$ sudo usermod -a -G spi,gpio pi

Log out and back in again to ensure that the group permissions are applied successfully.

Parallel

Beyond the power and ground connections, you can choose which ever GPIO pins you like to connect up your display. The following is one example for how to wire popular displays such as the Winstar WEH001602A.

Device Pin

Name

Remarks

RPi Pin

RPi Function

1

GND

Ground

P01-6

GND

2

VDD

+5.0V Power

P01-2

5V Power

3

NC

Not Connect

4

RS

Register Select

P01-26

GPIO 7

5

R/W

Read/Write

P01-14

GND

6

E

Enable

P01-24

GPIO 8

7

D0

Not Connected

8

D1

Not Connected

9

D2

Not Connected

10

D3

Not Connected

11

D4

Databus line 4

P01-22

GPIO 25

12

D5

Databus line 5

P01-18

GPIO 24

13

D6

Databus line 6

P01-16

GPIO 23

14

D7

Databus line 7

P01-13

GPIO 27

15

NC

Not Connect

16

NC

Not Connect

Note

  • You have the choice on whether to wire your device with 4 or 8 data-lines. Wiring with 8 provides a faster interface but at the cost of increased wiring complexity. Most implementations use 4 data-lines which provides acceptable performance and is the default setting for the parallel class.

  • Reading from the display is not supported by the :py:class:luma.core.interface.parallel.``bitbang_6800`` class so it needs to be connected to ground in order to always be set for writes (assuming the device uses logic-low for write).

Warning

  • Be careful with the logic level of the device you are using. Many SBCs including the Raspberry Pi uses 3.3V logic. If your device supplies 5Vs to one of the GPIO pins of an SBC that uses 3.3V logic you may damage your SBC.

Suggested Wiring

Note

  • The default GPIO for backlight is GPIO 18. This pin is also used for PCM_CLK in I2S. So when you use the I2S please specifying the new BCM pin number with the gpio_LIGHT argument.

PCD8544

LCD Pin

Remarks

RPi Pin

RPi Function

RST

Reset

P01-18

GPIO 24

CE

Chip Enable

P01-24

GPIO 8 (CE0)

DC

Data/Command

P01-16

GPIO 23

DIN

Data In

P01-19

GPIO 10 (MOSI)

CLK

Clock

P01-23

GPIO 11 (SCLK)

VCC

+3.3V Power

P01-01

3V3

LIGHT

Backlight

P01-12

GPIO 18 (PCM_CLK)

GND

Ground

P01-06

GND

ST7735

Depending on the board you bought, there may be different names for the same pins, as detailed below.

LCD Pin

Remarks

RPi Pin

RPi Function

GND

Ground

P01-06

GND

VCC

+3.3V Power

P01-01

3V3

RESET or RST

Reset

P01-18

GPIO 24

A0 or D/C

Data/command

P01-16

GPIO 23

SDA or DIN

SPI data

P01-19

GPIO 10 (MOSI)

SCK or CLK

SPI clock

P01-23

GPIO 11 (SCLK)

CS

SPI chip select

P01-24

GPIO 8 (CE0)

LED+ or BL

Backlight control

P01-12

GPIO 18 (PCM_CLK)

LED-

Backlight ground

P01-06

GND

ILI9341

No support for the touch-screen, leave the MISO and Touch pins disconnected. Depending on the board you bought, there may be different names for the same pins, as detailed below.

LCD Pin

Remarks

RPi Pin

RPi Function

VCC

+3.3V Power

P01-01

3V3

GND

Ground

P01-06

GND

CS

SPI chip select

P01-24

GPIO 8 (CE0)

RESET or RST

Reset

P01-18

GPIO 24

DC

Data/command

P01-16

GPIO 23

SDI(MOSI)

SPI data

P01-19

GPIO 10 (MOSI)

SCK or CLK

SPI clock

P01-23

GPIO 11 (SCLK)

LED

Backlight control

P01-12

GPIO 18 (PCM_CLK)

ST7567

This driver is designed for the ST7567 in 4-line SPI mode and does not include parallel bus support.

Pin names may differ across different breakouts, but will generally be something like the below.

LCD Pin

Remarks

RPi Pin

RPi Function

GND

Ground

P01-06

GND

3v3

+3.3V Power

P01-01

3V3

RESET or RST

Reset

P01-18

GPIO 24

SA0 or D/C

Data/command

P01-16

GPIO 23

SDA or DATA

SPI data

P01-19

GPIO 10 (MOSI)

SCK or CLK

SPI clock

P01-23

GPIO 11 (SCLK)

CS

SPI chip select

P01-24

GPIO 8 (CE0)

HT1621

LCD Pin

Remarks

RPi Pin

RPi Function

GND

Ground

P01-06

GND

VCC

+3.3V Power

P01-01

3V3

DAT

SPI data

P01-19

GPIO 10 (MOSI)

WR

SPI clock

P01-23

GPIO 11 (SCLK)

CS

SPI chip select

P01-24

GPIO 8 (CE0)

LED

Backlight control

P01-12

GPIO 18 (PCM_CLK)

UC1701X

The UC1701X doesn’t appear to work from 3.3V, but does on the 5.0V rail.

LCD Pin

Remarks

RPi Pin

RPi Function

ROM_IN

Unused

ROM_OUT

Unused

ROM_SCK

Unused

ROM_CS

Unused

LED A

Backlight control

P01-12

GPIO 18 (PCM_CLK)

VSS

Ground

P01-06

GND

VDD

+5.0V

P01-02

5V0

SCK

SPI clock

P01-23

GPIO 11 (SCLK)

SDA

SPI data

P01-19

GPIO 10 (MOSI)

RS

Data/command

P01-16

GPIO 23

RST

Reset

P01-18

GPIO 24

CS

SPI chip select

P01-24

GPIO 8 (CE0) Chip Select

HD44780 Parallel

Device Pin

Name

Remarks

RPi Pin

RPi Function

1

GND

Ground

P01-6

GND

2

VDD

+5.0V Power

P01-2

5V Power

3

NC

Not Connect

4

RS

Register Select

P01-26

GPIO 7

5

R/W

Read/Write

P01-14

GND

6

E

Enable

P01-24

GPIO 8

7

D0

Not Connected

8

D1

Not Connected

9

D2

Not Connected

10

D3

Not Connected

11

D4

Databus line 4

P01-22

GPIO 25

12

D5

Databus line 5

P01-18

GPIO 24

13

D6

Databus line 6

P01-16

GPIO 23

14

D7

Databus line 7

P01-13

GPIO 27

15

VDD

+5.0V Power

P01-4

5V Power

16

GND

Ground

P01-9

GND

Warning

A resister needs to be connected in series between pin 15 and the SBC to avoid excessive current draw and to control brightness. Many displays include a built-in resister for this purpose but if yours does not you will need to include an appropriately sized resister in your wiring between the SBC and pin 15 of the display.

HD44780 w/PCF8574

Device Pin Name

Remarks

RPi Pin

RPi Function

GND

Ground

P01-6

GND

VDD

+5.0V Power *

P01-2

5V Power

SDA

Serial Data Line

P01-3

GPIO 2 (SDA)

SCL

Serial Clock Line

P01-5

GPIO 3 (SCL)

Note

You should verify which pins from the PCF8574 are connected to the pins of the HD44780 display. There is no set standard for this wiring so different vendors will likely have used different approaches. This information will be needed when initializing luma.core.interface.serial.pcf8574.