The Optrex DMF50191N display

The LCD display

The DMF50191N is a simple monochrome 640 by 200 pixel LCD display. They were originally designed for Commodore portables, but those never materialized. They have drivers for the LCD matrix, but require additional logic to refresh the display. I have a display running on my parallel port. The parport isn't fast enough for good results, but you can at least get the idea.

A lot of what is presented here was originally put online by Jeroen Hilgers, but his website seems to have disappeared.

Pinout

There are 14 pads at the side of the display next to the intensity adjustment potentiometer. The pinout of these pads is as follows.

Displaying a frame

The display has 200 lines of 640 pixels. Each line is built by clocking 160 nibbles. Each nibble is latched on the low going edge of the column driver shift clock pin. When the first line is clocked in, start a new frame by clocking a 1 into the row driver. On the low going edge of the column driver data load / row driver shift clock the line will be displayed. The remaining 199 lines are displayed in the same manner, except that the row driver data input must be set to 0.

The potentiometer should be at the right of the display. The first nibble is on the left, the 160th on the right. Bit 0 of each nibble is the rightmost pixel in the nibble, bit 3 the leftmost.

The extra dots can be clocked with pins 11, 12 and 13. Simply clock 10 bits (1 for on, 0 for off), the first bit being at the right.

The negative LCD driver voltage must be around -18V to get a good image. The display requires about 50 frames per second to display a stable picture. That's 10000 lines per second, or 1.6 million nibbles.

Connecting the display to a parallel port

Connect the display as indicated in the table above. With my parallel port I can get about 15 frames per second, which is enough to get the idea, but it's clearly not enough. You will need some sort of microcontroller (e.g., a PIC) in order to get a stable image.