Electronic – Power-up Initialization of HD44780 LCD Module

hd44780lcd

I'm using an HD44780 clone LCD module a KS0066U. Everything works ok on the module except when I rapidly power cycle the device (on->off->on). For some reason a very short interruption in the power causes the display module to improperly initialize as a 1-line LCD instead of a 2-line LCD display. What would cause this behavior? Is there any way to prevent it in software?

EDIT: I'm using the display controller in 4-bit mode not 8-bit mode.

Best Answer

I changed my initialization code so that it sent the upper 4-bit nibble of the function set command twice. Following which I resent the upper 4-bit nibble followed by the lower 4-bit nibble. This does not match the datasheet which seems to indicate that you can send the upper 4-bit nibble then send the function set command upper 4-bit followed by lower 4-bit.

// Works sometimes pseudo-code
port=0x20;
e=1; e=0;
port=0x20;
e=1; e=0;
port=0xC0;
e=1; e=0;

// Works all the time pseudo-code
port=0x20;
e=1; e=0;
e=1; e=0;
port=0x20;
e=1; e=0;
port=0xC0;
e=1; e=0;

Related Solutions

Electronic – Debugging initialization of LCD with NT7605 driver

Oh, duh, I didn't read your code carefully -- your send SendLcdByte is wrong:

    void SendLcdByte( unsigned char command_0_or_data_1, unsigned char command)
{
    SendLcdUpperNibble( command_0_or_data_1, command);
    // send the lower nibble next
 // AS WRITTEN:
    P1OUT = (command & 0x0F) | (P1OUT & 0xF0);
 // SHOULD BE:
    P1OUT = ((command & 0x0F) << 4) | (P1OUT & 0xF0);
    Strobe( command_0_or_data_1);
}

Electronic – Why do almost all HD44780-based LCD displays use font pattern A00

Economy of scale.

Buy 100,000 chips that will do for all displays at say $0.10 each, or buy 50,000 of one chip at, say, $0.15 and 50,000 of another chip at $0.15 each.

^{(figures purely fictional - for illustration only)}

You do the maths.

While it's not 100% perfect for every display, it does mean that they are cheaper, which is good for all of us.

Best Answer

Related Solutions

Electronic – Debugging initialization of LCD with NT7605 driver

Electronic – Why do almost all HD44780-based LCD displays use font pattern A00

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