# LCD display driving method/waveform type

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#### jbeng

##### Member
If you want to drive the display so that all the segments are available to use, you'll need to use 30 pins -- 1 pin for the backplane and 29 for the segments that you want to control (one for each segment). Any unused segments should be connected to the backplane signal. Another way (a better way, I think) is to use a chip like National Semi's MM5453 LCD display driver chip and let it do all the dirty work. The problem is, I don't know if they still make that chip.

*edit* Good news! National still makes that chip. Here's a link to the pdf datasheet: http://www.national.com/ds.cgi/MM/MM5452.pdf. The link says MM5452, but the datasheet covers both the 5452 & 5453.
JB

#### Futterama

##### Member
jbeng, thanks for your reply, that chip looks like something I could use. But I think it is hard (expensive) to get in my country (Denmark). Actually they got is at farnell, but it's like $11 +$8 for shipping.

I guess the LCD signal type for this chip is Type-A.

And you are right, I probably need the PIC16F917 (40-pin) to use all segments if I use the PIC approach.

#### Nigel Goodwin

##### Super Moderator
Futterama said:
jbeng, thanks for your reply, that chip looks like something I could use. But I think it is hard (expensive) to get in my country (Denmark). Actually they got is at farnell, but it's like $11 +$8 for shipping.

I guess the LCD signal type for this chip is Type-A.

And you are right, I probably need the PIC16F917 (40-pin) to use all segments if I use the PIC approach.
Does the 16F917 include specific LCD support?, it's extremely important that the LCD is fed by accurate 50/50 AC signals, any DC offset in the drive will drastically shorten it's life. Commonly the LCD is driven by XOR gates, with one input from the data, and the other from an oscillator (guaranteeing the pure AC drive). Micro-controllers having LCD support include this type of system internally, as presumably does National's driver chip.

#### Futterama

##### Member
Nigel Goodwin said:
Does the 16F917 include specific LCD support?
Yes Nigel, the PIC16F913/914/916/917 has internal LCD drivers and gives the option to use two different kind of waveforms:

PIC16F91X datasheet said:
The LCDs can be driven by two types of waveform:
Type-A and Type-B. In Type-A waveform, the phase
changes within each common type, whereas in Type-B
waveform, the phase changes on each frame
boundary. Thus, Type-A waveform maintains 0 VDC
over a single frame, whereas Type-B waveform takes
two frames.

#### Nigel Goodwin

##### Super Moderator
Futterama said:
Nigel Goodwin said:
Does the 16F917 include specific LCD support?
Yes Nigel, the PIC16F913/914/916/917 has internal LCD drivers and gives the option to use two different kind of waveforms:
That should be fine then, I tried to download the datasheet this morning, but all I got was a blank page?

#### Nigel Goodwin

##### Super Moderator
Futterama said:
Nigel Goodwin said:
That should be fine then, I tried to download the datasheet this morning, but all I got was a blank page?
It should work, here is the direct link for the datasheet:

http://www.electro-tech-online.com/custompdfs/2006/01/41250E-1.pdf

I have, I downloaded the programming spec OK, then the datasheet just gave me a blank page?, perhaps a brief 'hiccup' at MicroChip?.

#### BrianG

##### New Member
Nigel Goodwin said:
I have, I downloaded the programming spec OK, then the datasheet just gave me a blank page?, perhaps a brief 'hiccup' at MicroChip?.
I just want to jump in here and say I had a similar problem with PDF documents when using Foxits free PDF viewer. However viewing with Adobe works fine. Not sure if this is your problem, but I thought I'd interject my \$0.02.

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