7-seg LCD Driver 96 elements?

[Mansoor]

Hi all,

I am working on a project in which i use many 7 seg LCDs. to control them i boguht the OM4068 LCD drivers made by NXP. since i needed to control more than 85 segments and each chip supported only 32 segmetns i must cascade the devices or have a separate connection between each of the drivers and the uC to control them.

The problem I am having is with the data sheets. in the data sheets found in this link, it is mentioned that the device can be connected to up to 96 elements. that is not possible since there are only 44 pins and only 32 are for segments. This can be seen in the image from the datasheet below



the second problem I am having is the way the shift registers inside the device are implemented, in the following picture you can see that each device has Three 32-bit shift registers. which i think is unnecessary since there can only be two values for each segments, on, or off. There are only 32 pins for 32 segments so what is the need for the other 64 bits?


here is the link to the data sheet again

My last but easiest of my problems is finding eagle footprints for this chip. I think it is crazy that people keep doing this menial task over and over. it is the same chip produced in millions.

thanks for all help!

[Soeren]

Hi,

32 segments x 3 Back Planes = 96 segments controllable.

Do you know how to use the back plane lines?

[Mansoor]

wow i did not know about that. I am guessing Backplanes must be some sort of Multiplexers. 32 inputs and two select lines and 96 outputs. thanks so much for the hint! I spent many hours on this thing without figuring that much out.

if u know of a website that describes this please share. thanks.

[Soeren]

Hi,

wow i did not know about that. I am guessing Backplanes must be some sort of Multiplexers. 32 inputs and two select lines and 96 outputs. thanks so much for the hint! I spent many hours on this thing without figuring that much out.

Yes, you might call them that, but they're meant for multi segment LCD's to cut down on pins.
It's like there's several LCD's in one and each has got a separate backplane and common segment lines.

if u know of a website that describes this please share. thanks.

The data sheet should be a good source.
Here is some info (near the bottom of the page).
A data sheet that might be helpful and here is one from Atmel.

[Mansoor]

Thanks so much. This really helped!