I'm currently trying to program the HD44780 from scratch in C. Noticed in its datasheet that for initialization, the exact same command has to be sent to thrice. I just curious what's happening inside the circuit. Why must a circuit be sent the same command so many times?

Is it because that this initialization sequence (i.e. same command sent 3 times at predefined intervals) unambiguously indicates to the HD44780 that this is really an initialization sequence; not a command or data sequence. Or does it have something to do with some design flaws in the HD44780 which requires the same exact command being sent thrice before it can properly initialize itself.

Thanks.

Hi Glendon,

I'm willing to bet that is just a redundancy thing. They want to make it relatively hard to reset the LCD with a mistake, or with an electrical glitch.

Humberto

Hi Humberto,

I kept thinking that the initialization can only be done once. From your reply, I realized that whenever the device sees the same data sequence, it would initialize itself again based on the new initialization sequence (and "parameters").

Now it makes sense to me. Thanks a lot!