Dot Matrix Display
From PinWiki
A Dot Matrix Display (or DMD) is pinball display technology that became prevalent from 1990 onward. While previous display technologies formed numbers and letters with discrete segments (or even reels), a dot matrix display is comprised of many dots which can be lit to form not only different numbers and letters, but also different fonts, as well as artwork and animation.
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[edit] Creating DMD Animations
DMD artists (also known as "dot guys") develop animation sequences for games one frame at a time. Frames must be created by hand, as simply scaling and converting a photograph (or a sequence of frames from a movie) does not yield good results. In an interview on TOPcast #28, dot artist Adam Rhine said that he has used Electronic Arts' Deluxe Animation (a program that was last updated in 1990) for every dot matrix project he has done, including recent Stern releases, as it is the only application suitable for the needs of a dot matrix artist.
Once the frames are ready, the artist would then send them to the programmer on the project, who could then display them on a DMD. It was not until much later that Williams built a "dot box" which would display frames sent to it over a parallel printer port, drastically improving the artist's ability to proof his work.
[edit] Technical Information
[edit] Resolution
The most commonly used dot matrix display resolution is 128 columns by 32 rows (128x32). Other dot matrix sizes have been used, such as 128x16 (on some Data East games), 192x64 (Data East and Sega), as well as 256x64 (for Capcom's Flipper Football). Each dot has only an 'on' and 'off' setting, so grayscale levels must be simulated by cycling dots on and off. According to dot guy Adam Rhine, Williams used four levels of brightness: 0%, 75%, 90%, and 100% on.
[edit] Control Interface
DMDs are generally controlled by a specialized controller board over six lines/pins:
- Display Enable
- Row Data
- Row Clock
- Column Latch
- Column Clock
- Column Data
A DMD, like other I/O systems in a pinball machine, operates as a matrix. In the case of a DMD, only one row is on at any one time. This means that the DMD must be updated continuously in order to display an image. For this reason, manufacturers generally recommend updating the entire frame at a minimum speed of 70Hz in order to avoid flickering. In order to display a row of dots, those dots must be fed into the DMD one dot at a time (using Column Clock and Column Data), and then stored (using Column Latch). Once the row of data is stored, the DMD is told which row to display (using the Row Data and Row Clock lines). A Display Enable line is also used in order to turn the entire display on or off. This can be used to turn off the display in the event of a failure, or (more commonly) to prevent blurring as the active row is updated.
The clock and data lines all feed to a series of serial-in parallel-out shift registers. As such, in order to control which row is active, a 1 (or high) must only be fed into Row Data once per frame. Pulsing Row Clock with Row Data set to 0 (or low) will advance (shift) the 1 down the rows while reading in 0's after it.
The order of operations for updating a full row of a DMD is as follows: (assumes a 128x32 resolution)
- Clock in a full row of 128 bits using the column data and clock lines. Hardware SPI (serial peripheral interface)[1] is best for this.
- Latch in the row of data bits by pulsing the Column Latch high.
- Disable the display.
- If this is the first row, set Row Data to high.
- Pulse the Row Clock low to advance the row data.
- Enable the display.
To update a full frame, the above sequence must be performed 32 times.
[edit] Manufacturing
Manufacturers include Babcock (under the Plasmadot trademark), Cherry Electronics, and Vishay-Dale. While these displays were originally manufactured using gas plasma technology, LED DMDs are becoming available from companies such as PinLED. In order to comply with RoHS[2], Stern is using LED displays in its export games.
