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HD44780 Hitachi Controller

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mongerson
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2009/04/16 17:07:21 (permalink)
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HD44780 Hitachi Controller

With a HD44780 Hitachi 16x1 LCD, my research indicates that CMOS logic levels are required. The specific datasheet for the LCD device I'm trying to interface with can be found here. I was hoping someone might be able to provide their interpretation of this data sheet for me and let me know if for sure if the logic high must be approximately 5V (CMOS logic high). I'll use some pull-up resistors for interfacing with the dspic33fj12gp202 (3.3V TTL levels) if so. Another concern of mine is that only some of the pins on the dspic33fj12gp202 are 5V tolerant, which means I may have to use those pins if i'm to reconfigure an output as an input for control purposes (in the case of a busy flags etc.). If pull-up resistors are required, I'll have to calculate a value such that the slew rate won't affect the accuracy of the switching. I very much appreciate any help I can get on this project.

Thank you,
- Michael
#1

10 Replies Related Threads

    Steven37
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    RE: HD44780 Hitachi Controller 2009/04/16 18:02:22 (permalink)
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    Hi,

    Why not just use an LCD module that runs on 3.3V ?
    When I was researching a project that was going to run on 3.3V I found some LCD's that were suitable, haven't got any current info on 3.3V LCD's because my project ended up running on 5V as there were several other IC's that we needed that were 5V only.

    Regards Steve.
    #2
    mhanuel
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    RE: HD44780 Hitachi Controller 2009/04/16 22:10:13 (permalink)
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    Steven37 you are right, there are already 3.3V LCD.

    I know Newhaven Displays have them, check http://www.newhavendisplay.com.
    Maybe the controllers are different part numbers like KS0066U but essentially they are compatible with the 44780...
    By the way digikey distribute some parts from them, not sure if the 3V devices, anyway you could place an order directly with them...

    Hope that help you.

    Best,
    #3
    mongerson
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    RE: HD44780 Hitachi Controller 2009/04/17 10:32:33 (permalink)
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    So does anyone know if this device must have around 5V for a logical high?

    Vih1, and Vil1 suggest 2.2 and 0.3 being the minimum input voltage (respectively), but from the datasheet i'm having a difficult time determining if this is indeed for the data pins 0-7.


    #4
    MBedder
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    RE: HD44780 Hitachi Controller 2009/04/18 02:12:25 (permalink)
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    See my post - it explains how to interface any HD44780 (or its clone) based LCD display to a 3V MCU without any level translation. I also recommend using a 4-bit interface mode with only two control lines - RS and E (R/W line is tied low permanently, no LCD status reads used, use a predetermined delay instead).
    #5
    mongerson
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    RE: HD44780 Hitachi Controller 2009/04/20 10:20:41 (permalink)
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    OK, so by tying the R/W line to GND, I will always be writing to the LCD. I'm using the timing diagram in conjunction with the __delay32 m30 function to figure out the timing which means I'll never need to read the BF (busy flag). Since I'll always be writing to the LCD, it will not be necessary to have any input to the DSC from the LCD, all of the DSC pins will be outputs and the output voltage will satisfy the requirements of the HD44780 for both the data and control lines.

    If I were to either read the BF or the Data from the LCD on the DSC, I would have to be sure that the pins that I was using as inputs from the DSC were 5V tolerant, but in this case that issue won't come up.

    Does this make sense??

    Thanks,
    - Michael
    #6
    Neiwiertz
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    RE: HD44780 Hitachi Controller 2009/04/20 11:20:31 (permalink)
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    Vih1, and Vil1 suggest 2.2 and 0.3 being the minimum input voltage (respectively), but from the datasheet i'm having a difficult time determining if this is indeed for the data pins 0-7.
    I had a quick look i think it is possible to use DB0 to DB7 lines attached to 3V3 DSC:
    Electrical Characteristics

    Output Voltage(1) VOH1 Min 2.4
    DB0 to DB7         VOL1 Max 0.4

    For other lines of the LCD i could read high level 0.9VDD If this pin is attached to 3V3 DSC from lcd
    you could use resistor divider to translate back to 3V3 IO level.

    Output Voltage(2) VOH1 Min 0.9VDD
    except DB0 to DB7 VOL1 Max 0.1VDD

    Flying With --|Explorer 16|HardWare|SoftWare|-- Fav(s) Gallery Lists
    #7
    mongerson
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    RE: HD44780 Hitachi Controller 2009/04/20 14:44:18 (permalink)
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    One other thing... with 4-bit mode, should I tie the 4 unused data pins on the LCD to ground?
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    Neiwiertz
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    RE: HD44780 Hitachi Controller 2009/04/20 14:59:20 (permalink)
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    I am just started todo simular by interfacing the LCD at Explorer16 (E16) by try using 4-Bit mode. It is wisdom to not left floating pin(s) in general, i guess it won't hurt to pull down the lower nibble DB0-3.

    I must have a look at the HD44780 spec for this (but i feel this lower nibble DB0-3 is "don't care" by the HD44780 as soon when it is init to work at 4-Bit mode)

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    #9
    mongerson
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    RE: HD44780 Hitachi Controller 2009/04/20 15:46:41 (permalink)
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    So in the case of running in 4-bit mode, can the LCD be initialized into 4-bit mode with only having the following (6) pins connected: <DB 4-7>, E, & RS (assuming R/W is tied to gnd)?
    #10
    MBedder
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    RE: HD44780 Hitachi Controller 2009/04/21 00:26:24 (permalink)
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    Yes, exactly. As of unused data pins - the HD44780 has internal pullup resistors so you can leave these pins unconnected.
    #11
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