Arduino library for Noritake GU800-series graphical VFDs

This library provides an Adafruit_GFX drawing interface for use with Noritake GU800-series graphical vacuum-fluorescent displays, as well as exposing the display's native command set.

While I have only tested this library using a GU128X64-800B display, the datasheets of other GU800-series displays suggest that it should be possible to adapt this library to work with other similar models by changing the GU800_WIDTH and GU800_HEIGHT macros as appropriate.

Since the GU800 provides no means to read the contents of its framebuffer, and it is only possible to write whole bytes, rather than manipulate individual pixels, this library draws to a 1kbyte framebuffer on the Arduino, and transfers it to the display when the display() method is called (similar to the ubiquitous I2C SSD1306 displays).

Datasheet Links

GU128X64-800B: https://media.digikey.com/pdf/Data%20Sheets/Noritake%20PDFs/GU128X64-800B.pdf

Notes

Power

Power supply is 5VDC (higher-voltage DC for the anode and grid, and AC for the filament, are produced by an onboard converter). Rated max. current is 900mA, on my unit I observed ~500mA idle current with no pixels lit, ~650mA with all pixels lit. This is too high to power over USB, but just barely within the allowable limits of the Arduino's onboard 5v regulator, so it may be possible to power from an Arduino connected to an external PSU.

Input voltage tolerance is rather narrow; a sag to 4.7v is enough to cause the display to reset. Rated long-term max. input voltage is 5.2v, absolute max. is 6.5v.

Output levels are 5V TTL, input thresholds not suitable for 3.3v.

Connectors

Jumpers J1 and J2 set the interface type:

J1	J2	Type
Open	Open	8080 parallel (default)
Closed	Open	6800 parallel
Any	Closed	SPI

The power connector is 3 pin JST B3B-XH-A.

Pin	Description
1	5V DC
2	Test
3	GND

Grounding the test pin illuminates all pixels on the display.

The data connector is a standard 2x13 0.1" header, with keyed shroud. Even numbered pins (except 26 which is /RESET) are grounds. Assignments for the other pins depend on the interface type set by J1 and J2 - refer to the datasheet for full descriptions.

Signals

In addition to the interface-specific signals, the following signals are used:

Name	Description
/CS	Chip-select. Active-low.
C/D	Command/Data select. Set high to write command, set low to write data.
/RESET	Reset display. Active-low. Must be held low for > 1.5ms.
FRP	"Frame pulse". Driven high while display is being refreshed.

SPI Interfacing

Data is transferred over SPI MSB-first, using mode 3 (clock idles high, data valid on rising clock), with a maximum clock rate of 5 MHz. /CS must be deasserted after every byte transferred.

/CS must be asserted at least 40 ns before starting the clock, and must remain asserted at least 150ns after the last clock pulse. C/D is sampled on the last clock pulse and must be held until C/D is deasserted.

Note that I experienced instability at higher SPI speeds with the display connected via a breadboard. Connect the display directly for best results, or reduce the SPI clock rate in GU800_GFX.h.

Buffer format

Data is written to the GU800 as bytes, with each byte representing a column of eight pixels, LSB at the top. The framebuffer maintained in this library follows this format, in row-major order (8x 8-pixel-tall rows of 128 columns each).

Refresh Rate / Sync

The display refreshes at ~140 Hz, and outputs the FRP signal as a kind of 'vertical blank' signal. According to the datasheet, the optimal time window to write to the active page, or flip pages, is within 6ms of FRP going low.

In practice, animation seems to be smooth enough without caring about sync pulses, but it might be worth looking into.

Constructor

SPI

GU800(int csPin, int dcPin, int resetPin)

csPin: pin connected to /CS
dcPin: pin connected to D/C
resetPin: (optional) pin connected to /RESET

Parallel

TODO

API

As well as the standards Adafruit_GFX drawing primitives, the following methods are exposed:

begin() - Reset and initialize display. Must be called before use.
display() - send the Arduino framebuffer to the display. Must be called after drawing operations in order to show the result.
clearDisplay(bool display=false) - Clear framebuffer. If display is true, also blank the display.
invertDisplay(bool invert) - enable or disable reverse-video mode.
dim(uint8_t level) - Set display brightness; 0=minimum, 16=maximum.
displayOn(bool fade) / displayOff(bool fade) - turn display on and off. If fade is true, use a fade-in/out effect. Display contents are preserved.

The full command set is available as public methods, but should be used with care since they could put the display into a state not expected by the library.