piclist 2002\02\10\044006a >
Thread: CHALLENGE: 4x4 keyboard and LCD with 1 port = 8 bits
picon face BY : wouter van ooijen & floortje hanneman email (remove spam text)

I might be blind but I don't see the big problem. The high nibble drives the
control lines, and (via D+R) the key rows. The low nibble drives the LCD
data pins and reads the key columns (use pull up or down R's). The only
snatch is that to scan one row you'll have to toggle E, which can cause an
operation on the LCD. To get around this problem:

- make sure the operation is a no-op, like reading, or writing to a location
that does not matter (maybe one of the user-defined characters)
- reverse the operation immediately afterwards (for instance erase the char
just written)
- you have a pin 'left over' (or two, when you don't read). Use them all to
drive E in and-fashion (you can use a D-R and gate, I think that does not
count as active?)

It is a pity I have no time to try this (one-hand typing with a baby in the
other arm is difficult enough).

Wouter van Ooijen

Van Ooijen Technische Informatica: http://www.voti.nl
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<018201c1b1f1$7ce37280$0500a8c0@home> 7bit

See also: www.piclist.com/techref/io/lcd/pic.htm?key=lcd
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Subject (change) CHALLENGE: 4x4 keyboard and LCD with 1 port = 8 bits

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