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Help on interfacing CFAG 5V LCD with 3.3v uC

gasparweb

New member
Hi!:

Im working with a couple of GLCD, the CFAG240128L-YYH-TZ and the CFAG240128L-STI-TZ.
I will drive these GLCD's with LPC2148 uC, wich has a logic level of 3.3V.
The LPC2148 pins are 5V tolerant (Vpin max = 6V).
Since your GLCD's dont meet the TTL level specifications:
GLCD level: Vih min = 2.8 (?)
uC level: Voh min = 2.9 (at -4mA):

1. Can i use the GLCD without level shifting?
2. Which is the current consumption of I/O pins of the GLCD: I input high max (Iih max)?
3. Please tell me the ways to maximize the noise margin. (IC, pull-up, etc)
4. Any advices to ensure fiability on the interfacing?

Thanks in advance!
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CF Tech

Administrator
For this kind of question, the best reference is the controller data sheet:

http://www.crystalfontz.com/products/128128a/Toshiba_t6963CFG.pdf

We try to put all we can in our LCD module data sheets, but if you want to "push" the controller, it is best to consult the controller data sheet directly.

Sometimes the easiest thing to do is run the display controller at the 3.3v. You still need to worry about generating enough negative voltage to get Vlcd large enough, but that may be a simpler problem than the translator. In the case of the T6963, it is not specified for 3.3v, so you would be in kind of unknown territory there. Generally the type of CMOS circuits like this will run at the lower voltage, but if they are not characterized at the lower voltage, you would have to do some experimentation to make sure it works in all cases.

I think the safest way to proceed would be to go ahead and just use some "real" 3.3v to 5v converter chips.

There is an interesting page here:

http://www.interfacebus.com/Design_Translation.html

which uses a 47LV2445.

These two links from TI's site also look good for learning about it:

http://focus.ti.com/paramsearch/doc...log&familyId=886&uiTemplateId=NODE_STRY_PGE_T
http://focus.ti.com/analog/docs/techdocsabstract.tsp?familyId=886&abstractName=scea035a

In our demo board for a 3.3v display in a 5v system:

http://www.crystalfontz.com/products/cfaxzifdemo/index.html

We used a SN54HC574.

Poking around on the web might come up with some good information:

http://www.google.com/search?q=t6963+3.3v
 
GLCD level: Vih min = 2.8 (?)
uC level: Voh min = 2.9 (at -4mA)
If you are only driving the LCD inputs from the uC, then there won't be anywhere near 4 mA load on the uC, so that spec is not relevant. Driving a cmos input, the uC output should be the full 3.3 V.

I use a Zilog 3.3 V CPU to drive several kinds of CFA 5 V graphic and character LCDs, with no problems. Only if you needed the maximum robustness under all conditions is it worth the trouble to add the voltage translator ICs (IMHO).
 
Last edited:

gasparweb

New member
Happy conusmer x2

Thanks for you accurate, complete and fast response!

Like you say, the uC drive 3.3V on the bus, without problems.
The interfase without "level-shifiting" metods seems to work ok!

Now, i have others problems, but, this is not the place to post it.

Thanks again CF Team!
 
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