Using the Hitachi LMG7422PLFF LCD

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Display information

This is a 240x128 Liquid crystal display from Hitachi. It uses the T6963c controller from Toshiba and is backlit via a single white CCFL along the bottom of the screen. This display uses the well known T6963c controller, so it is not going to be a problem to hook it up to the PC parallel port and start using some of the currently available software. However, by default the font size of the chip is hard-wired and set to 8x8. This is not any good for using the display with any of the current software, as the standard is 6x8 (5x7 with a spacing pixel). As it is hard wired into the display, we have to alter where some of the pins are connected on the controller chip on the back of the LCD. We also need to make a DC-DC Converter for the LCD to power the LCD Drive, as it does not have one on board. All the information you need to get this LCD rolling is contained in this document.

Selecting the correct font size

As I said above, we need to re-connect some of the pins of the T6963c controller chip on the back of the LCD. I'd like to thank Zotty for helping me discover that this was the problem. We need to move 2 pins. The following image shows the T6963c controller as viewed from the top.


The pins that we are interested in are pin 6 - 'MD2' and pin 9 - 'FS1'. As you may have guessed, FS stands for font select, and the MD pins are for selecting the correct size of the display. By default MD2 is set to H (+5v) and FS1 is set to L (0v). We have to change MD2 to L (0v) and FS1 to H (+5v). This will set the correct display size and set the font size to 6x8.


The T6963c controller chip is circled in red in the image above.


Hopefully you can see the modified pin connections in the above image. The technique I used was to bend pin 6 (MD2) upwards and solder it down on to the top of pin 5, as I discovered this pin was set to ground already, so naturally, connecting them together meant that they were both then connected to ground (0v). As for pin 9 (FS1), I unsoldered the pin from the PCB and lifted it up, then I was able to solder on a lead to connect it to +5v. Extreme care is required when making these connections, because if the pins should break off from the controller, then the LCD will be unusable.

If you have done that successfully, then the font size should now be set to the correct size, 6x8.

DC-DC Converter

We need to build a DC-DC converter for this LCD as well, to supply the required voltage for the LCD drive (-20v). A DC-DC converter is simply a device that will take a +5v input and give the negative voltage you require. The schematic for the converter that I used is shown below (click for full image).

MAX629 DCDC.gif

You can obtain the MAX629 IC as a free sample from the manufacturers website.

Wiring it to a parallel port

Seeing as it is a standard T6963c based LCD, we can use standard T6963c wiring diagrams, however, a couple of adjustments need to be made to allow this LCD to work correctly. This is a table of the pinouts of the LCD.

Pin # Symbol Function Connection
1 Vss Ground 0v
2 Vdd Logic Power +5v
3 V0 LCD Drive See diagram
4 C/D Command/Data Parallel Pin 17
5 WR Write Parallel Pin 16
6 RD Read Parallel Pin 14
7-14 DB0-DB7 Data Lines Parallel Pin 2-9
15 CE Chip Enable Parallel Pin 1
16 RET Reset See diagram
17 Vee N.C No Connection
18 D.Off N.C - Display on No Connection
19-20 N.C. No Connection No Connection

Wiring diagram below.


First published @ on 04/01/2003. If you successfully got yours working, I recommend LiquidMP3

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