MOP-AL204A Logic Levels

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Cliff Huston
LCD?
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Joined: Mon Jul 20, 2009 9:54 pm
Location: Saratoga, CA

MOP-AL204A Logic Levels

Post by Cliff Huston » Mon Jul 20, 2009 10:00 pm

I am redesigning a micro-controller board for an industrial client that has been using your MOP-AL204A LCD display, which if I understand correctly, uses the S6A0069 LCD controller chip. The micro-controller board that the client was using(obsolete), used 5V logic to drive the display bus. The new design is using 3.3V logic (LVTTL, 5V tolerant) to drive the display bus. In both cases the display supply voltage is 5V. The question is whether or not voltage level translation is needed for the new design on the display bus. Reading the MOP-AL204A specification, the answer seems to be yes (logic high: 0.7x5V=>3.5V); but reading the S6A0069 specification, the answer is no translation needed (logic high: >2.2V).

Which is correct?

MOP-AL204A Specification:
Supply Voltage: 4.5V min., 5.0V typ., 5.5V max.
Input High Voltage: 0.7 Vdd min., Vdd max.
Input Low Voltage: Vss min., 0.3 Vdd max.

S6A0069 Specification:
Supply Voltage: 4.5V min., 5.5V max.
Input High Voltage: 2.2V min., Vdd max. (except OSC1)
Input Low Voltage: -0.3V min., 0.6 V max. (except OSC1)

Supply Voltage: 2.7V min., 4.5V max.
Input High Voltage: 0.7 Vdd min., Vdd max. (except OSC1)
Input Low Voltage: -0.3V min., 0.55 V max. (except OSC1)
Cliff Huston
Propeller Head Design

Paradigm
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Post by Paradigm » Tue Jul 21, 2009 3:46 pm

The answer is unfortunately a little complicated. The data in our datasheet is provided by the manufacturer of the displays, which uses a S6A0069 compatible chip (which is in turn HD44780 compatible). So simply digging up a single S6A0069 datasheet may not be enough.

I would be surprised if the display did not operate at the lower voltages, however you will be dramatically reducing your noise margin. For reliable operation, a 0/5V swing would be ideal, and with a micro-controller that is 5V tolerant, it's actually quite easy. Tie all the I/O lines to 5V through a 1-10k resistor. Then to output a low logic level, simply output a 0. To output a high logic level, change the pin to an input, allowing the pin to float high due to the input. Many micro-controllers even have pull-up resistors that would mitigate the need for external parts.
James McTavish, P.Eng
Director of Engineering
Matrix Orbital

Raquel
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Post by Raquel » Tue Jul 21, 2009 4:48 pm

If I may add to James' reply, we have the HD44780U data sheet on our site here. Please use it for your reference for control and timing diagrams.

As per electrical characteristics, please use the MOP-AL204A-Edata sheet.

Thanks,
Raquel Malinis
Design and Development
Matrix Orbital

Cliff Huston
LCD?
Posts: 2
Joined: Mon Jul 20, 2009 9:54 pm
Location: Saratoga, CA

Post by Cliff Huston » Wed Jul 22, 2009 5:26 am

Hi James,

Thanks for the reply.

I expect the client will ask me to find a display that is specified to work with the LVTTL signals, instead of messing with the open collector hack (the client is doing the software support). He only uses 200 units a year, so no big deal.

You might consider forwarding my question to the manufacturer of the display - you may find that this product is more competitive than you think and is simply suffering from a crappy data-sheet. 5V logic is so . . . last century. Even 3.3V logic is getting to be a bit old fashion.

Since I have some of your displays, I plan on trying them on the prototype and will let you know if I see any problems using LVTTL signals.
Cliff Huston
Propeller Head Design

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