The ER-OLEDM032-1 is a 256x64 graphical OLED display. Each pixel is a 4-bit gray-scale value.

http://www.buydisplay.com/default/oled-3-2-inch-displays-module-companies-with-driver-circuit-blue-on-black

The display board has four different interface options. I used the 4-wire SPI mode in this project to connect the display to a Raspberry Pi.

The display has four different interface modes selected by jumpers on the back of the board. The jumpers are actually two 0 Ohm surface mount resistors you must move to select the desired interface. See the interface documentation for details.

https://github.com/topherCantrell/ER-OLEDM032-1/blob/master/docs/ER-OLEDM032-1_Interfacing.pdf

The interface options are:

• 8-bit parallel for 6800 series microprocessor
• 8-bit parallel for 8080 series microprocessor
• 3-wire SPI interface
• 4-wire SPI interface

My board arrived with the jumpers set for "8-bit parallel for 6800 series microprocessor". I carefully changed the jumpers to "4-wire SPI interface".

Usually "4-wire SPI" means that both MOSI and MISO wires are used in a bidirectional connection. Usually "3-wire SPI" means that MOSI and MISO are combined into a single SI/SO line that handles communication.

The SPI interface to the ER-OLEDM032 never sends data back to the processor. Despite the "3-wire" and "4-wire" terminology in the display documentation the interface is ALWAYS the traditional-4-wire-SPI, but the MISO wire is ignored.

The term "4-wire" in the documentation refers to an extra signaling wire that is unrelated to the SPI interface.

You talk to the display by sending a COMMAND byte followed by several DATA bytes. You must tell the display whether the byte you are writing is to be interpreted as a COMMAND or DATA. In the "4-wire" interface option you use a separate wire to select COMMAND or DATA. In the "3-wire" interface option you send the select as the first bit in a NINE bit SPI sequence.

The native SPI library on the Raspberry Pi has trouble sending 9-bit bytes. I used the extra COMMAND/DATA wire and normal 8-bit SPI writes.

The display uses a Solomon Systech chip, the SSD1322, to drive the display. The CMOS chip has many control registers and command sequences described in the reference manual:

https://github.com/topherCantrell/ER-OLEDM032-1/blob/master/docs/SSD1132.pdf

The chip is designed for a 480x128 OLED display, but its registers can be configured to work with the 256x64 display.

The company has published demo code for the 256x64 display. The code is written in C. The code includes the initialization sequence and routines to draw on the display.

https://github.com/topherCantrell/ER-OLEDM032-1/blob/master/docs/ER-OLEDM032-1_DemoCode.txt

I translated this C code to Python for use on the Raspberry Pi. See pi/RPI_OLED.py in this project.

The demo code initializes the display and draws several screens. Then it enters a loop allowing you to type in new contrast values (0 to 255).

These photographs of the running display (pardon the poor quality) show several of the screens from the demo.