question about open-drain-port

M

made

Guest
Hy

I´d like to connect a lcd (ttl 5V ;generic) to my microcontroller(cmos
3.3V, at91eb55).
I understand that it would be a good idea to use a open drain output
to drive the lcd. But what happens if I set the io-pin to input mode to
read the status register from the lcd ? Can the lcd drive the voltage
level ?


.....+5V.....
.....|.......
...._|_......
....|R|.......
....---.......
.....|........
.....|..._____
.....|...|....|
--------|.LCD|
.........|....|
.........|....|
.........------
 
if the lcd has TTL input, you can drive the lcd with 3.3V without a
open-drain! because the Vih (Input Voltage High) begin at about 2V! and
certainly the microcontroller is input 5V tolerant!
excuse me for my english!

"made" <pilzimkopf@gmx.de> a écrit dans le message de
news:c5ui8j$288$07$1@news.t-online.com...
Hy

I´d like to connect a lcd (ttl 5V ;generic) to my microcontroller(cmos
3.3V, at91eb55).
I understand that it would be a good idea to use a open drain output
to drive the lcd. But what happens if I set the io-pin to input mode to
read the status register from the lcd ? Can the lcd drive the voltage
level ?


....+5V.....
....|.......
..._|_......
...|R|.......
...---.......
....|........
....|..._____
....|...|....|
--------|.LCD|
........|....|
........|....|
........------
Click to expand...
 
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