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'LCD module 4 bit mode and multiplexed Key board'
2006\07\11@142610 by louis frias

I need suggestions .. I would like the time share the 4 I/O lines needed to
to an LCD module HD44780 in the 4 bit mode …and be able to multiplex a cross
3x4 or 4x4 switch key board in a similar manner as I do with multiplexed 7
LEDs. I only need 10K and a 100k isolator resistors to be able to do a quick
kbd mux
scan between 4 digit plexes. I understand that the 4 bit LCD module I/O line
are tristatable.
I can not find any were a clear indication if the E (enable) line of the LCD
module will
allow me to do a quick scan of common connected switch matrix to these 4 bit
I/O lines
in a manner that it will not interfere with the switch scan or the LCD
module itself.
Any suggestions ??????????????????

2006\07\11@145247 by Robert Rolf

picon face
The E line of the the LCD module is effectively a 'device enable'.
When not enabled, it ignores everything on the input pins so you
should have no trouble multiplexing the pin functions.

If you are not reading back anything (e.g. busy status or cursor info)
you can tie the R/W line to write mode as well and know that the
device will never drive the pins.


louis frias wrote:

{Quote hidden}

> Any suggestions ??????????????????

2006\07\11@151219 by louis frias

Thanks A LOT !!!!!!! I will wire it up and see how it goes. I just thought
it would be worth asking
before wasting a lot of time ....only to find out that my hunch was right !!
I have never used the 44780.........

Thanks again    Lou Frias IMC Instruments
visit us at

{Original Message removed}

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