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[Lcdproc] strange characters


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  • From: joris AT robijn.net (Joris Robijn)
  • Subject: [Lcdproc] strange characters
  • Date: Wed Oct 31 15:05:01 2001

> The resistor "R" should be a pull-up resistor to ensure, that "EN" is
> always up, especially when the computer is switched off. However, this
> does not seem to always work...

What you want is probably hard to establish in a way that always
works on every port. The state that the LPT port is in while booting
can be undetermined. You are trying to keep the EN line in a known
state by pulling it up. When the TL light starts it can generate
quite some interference, and because the ouput pins on the LPT port
are not actively keeping the line low or high (relative high
impedance), the voltage on the line can swing a bit. That lets the
display think that it is addressed (EN line).

First of all, you should pull the line low, because the input is
active high. However, the resistor-trick might not work because
_some_ LPT ports cannot 'source' enough current (that means current
from the VCC side). You can just try some values for the resistor. If
you have given the resistor a too small value the LCD will not
respond anymore, because the line cannot get high enough. Most modern
ports can source at least 5mA, so you can use 1k to pull it low. I
would say just try some values, to start with 1k, and switch the
light on and reboot and try everthing.

I like this kind of problems :)

Joris

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Joris Robijn
<joris AT robijn.net>
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