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Topic: Newhaven NHD-C0220AZ-FSW-FTW (Read 4 times) previous topic - next topic

floresta

#25
Dec 08, 2012, 05:57 am Last Edit: Dec 08, 2012, 06:02 am by floresta Reason: 1
Quote
I set E, RW low and RS stays low to write commands (setting mode to 1 means RS low, if mode sees a 0 then RS sees a 1 and thats when we write to  DDRAM), then E goes high, data gets pushed through and then E goes low and high...this is how I read it. I hope that is correct.


That is not correct.  The diagrams on page 8 of your datasheet show essentially the same sequence of events as shown on the datasheets for all of the other controllers (I didn't check the actual times, just the sequence).  My description in the last paragraph of reply #1 describes what is happening.  

Since the actual data transfer occurs on the falling edge of the 'E' pulse you should change the logic analyzer configuration to put that point near the center of the display.  That way we can check the what is happening both before and after the data transfer.

I didn't read your code, but most likely it requires some changes.  Make sure you use the 'Code' tags when you post your corrected code.  You should consider just driving R/W low at the beginning of your program and leaving it there since you are not ready to deal with the busy flag at this point.


Don

floresta

Quote
That makes absolutely no sense at all and is very likely to damage the display. The contrast pin is V5, not Vdd.

What doesn't make sense?

When you are running the device from a 5 volt supply the supply voltage for the controller is 5 volts above GND and the supply for the LCD (frequently called the contrast voltage) is 4.4 volts below that (at 25C).  This puts the contrast pin at 0.6 volts above GND.

When you are running the device from a 3.3 volt supply, and if the contrast voltage is still 4.4 volts (or so) below that, then the contrast pin must indeed be negative with respect to GND. 

I don't think there is any reason to suspect that this may harm the device as it is quite normal for an LCD to require a negative contrast voltage, especially those designed to run at low temperatures.


Don



liudr

I would recommend OP to use UNO and 5V, follow a standard tutorial, test the display with liquidcrystal library to make sure it works. Don't use your own code or 3.3V Only creates more uncertainty.

Papa G


Quote
That makes absolutely no sense at all and is very likely to damage the display. The contrast pin is V5, not Vdd.

What doesn't make sense?

When you are running the device from a 5 volt supply the supply voltage for the controller is 5 volts above GND and the supply for the LCD (frequently called the contrast voltage) is 4.4 volts below that (at 25C).  This puts the contrast pin at 0.6 volts above GND.

When you are running the device from a 3.3 volt supply, and if the contrast voltage is still 4.4 volts (or so) below that, then the contrast pin must indeed be negative with respect to GND. 

I don't think there is any reason to suspect that this may harm the device as it is quite normal for an LCD to require a negative contrast voltage, especially those designed to run at low temperatures.


Don





While what you say is true for some LCDs and in particular for LCDs designed to run at low temperature, I don't know if that applies to this COG display with the NT7605 controller. I say that because the controller data sheet says:

Quote
All voltage values are referenced to GND = 0V
V1 toV5, must maintain VDD ?V1 ?V2 ?V3 ?V4 ?V5?GND.(my emphasis)

V5 is the contrast voltage for this display and the data sheet specifically calls for it to be positive with respect to ground.

The warning in my comment was because of this statement:
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In a 3.3v environment, you will need to create a negative voltage (-1v or more) and apply it to the contrast pin (Vdd in your case).

Vdd is not the contrast pin and accidentally hooking it to a negative voltage could well damage the display.

floresta

Quote
Quote
All voltage values are referenced to GND = 0V
V1 toV5, must maintain VDD ?V1 ?V2 ?V3 ?V4 ?V5?GND.(my emphasis)

V5 is the contrast voltage for this display and the data sheet specifically calls for it to be positive with respect to ground.

Good point, but that is from the controller datasheet and we are talking about the display.  I'm not sure it would apply.

I am not sure that the 'V5' in your quote above and the 'V5' designation for pin 2 of the LCD module are one and the same.  I have never seen the 'contrast' pin labeled V5 before, but then again I've never seen it implemented on pin 2 before either.


Don




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