The LCD needs a minimum voltage to change status. A module designed for
5 volts (the most usual) has an LCD with a threshold higher than 3.3 V, so if you supply the module (and hence the HD44780) with 3.3 V the LCD will stay blank.-- Saludos Miguel Giménez
I don't remember anyone ever suggesting that you supplied the module with 3.3v.as a POWER SUPPLY.
The argument was whether the 3.3v *logic output* of the GPIO would be enough to drive the chip when the chip was being supplied with 5v.
The answer is, on the spec, yes.
-- Ineptocracy (in-ep-toc?-ra-cy) ? a system of government where the least capable to lead are elected by the least capable of producing, and where the members of society least likely to sustain themselves or succeed, are rewarded with goods and services paid for by the confiscated wealth of a diminishing number of producers.
Are R-Pi GPIOs 5-volt tolerant?. If not, you can connect the module only if you don't read from it. This means using a delay instead of checking the BF flag before writing.
-- Saludos Miguel Giménez
No, they are not
Exactly. We need to use ist either in readonly mode or add an additional level converter chip.
Sven
-- "Those who do not understand Unix are condemned to reinvent it, poorly" (Henry Spencer) /me is giggls@ircnet, http://sven.gegg.us/ on the Web
In 4-bit mode you can do it with just eight resistors.
-- Saludos Miguel Giménez
No need for resistors in readonly mode.
See schematic at adafruit:
Sven
--
The main thing to note is that when you choose open source you don't
get a Windows operating system.
(from http://www.dell.com/ubuntu)
/me is giggls@ircnet, http://sven.gegg.us/ on the Web
They're not 5v tolerant - well - they might be for a few nanoseconds ;-)
Most drivers I've seen on most microcontrollers don't bother with reading the status bit anyway - when I put mine together I tied the r/w pin to 0v forcing the display into read only mode. The timing for the long-time operations is published anyway (e.g. clear, home) so trivial to impement. Only 6 wires needed for 4-bit mode to the display. I also worked out that you can connect multiple displays to the Pi too - just need one more wire per display and off you go (that was a specific request from a client).
The question in-hand is whether they ought to be part of the kernel or have some other driver that you can use to use "standard" curses, etc. libraries, but hey, they Pi is all about programming and interfacing (to a lesser degree), so just get on & program... And who's to say (e.g.) my C driver code isn't "standard" anyway - it's my standard ;-)
Gordon
I was wondering pretty much the same thing. What's wrong with a user-mode app taking input from a named pipe, or if it really must be a terminal a pty? No need at all for kernel programming with all the hassle that imposes.
-- Andrew Smallshaw andrews@sdf.lonestar.org
What I don't know is if there's a sufficiently generic GPIO framework that we can say:
Take hd44780lcd.ko Plug in GPIO 73 into R/w Plug in GPIO 34 into D0 GPIO 45 is an interrupt Now create /dev/hd44780lcd0
and make it work, given that the 'plumbing' between the LCD driver module and the SoC is something the user controls. From what I've seen, OpenWRT makes a meal of this because every router, even using the same SoC, has a different pin to enable wifi power/talk to the SPI flash/drive the LEDs, and every router has a different C file in the kernel to describe this. But it doesn't work if the user can change that mapping.
Theo
Good point: However, I don't (yet) need an HD447800 or equivalent. When I do, I'll want something like the display used in the device formerly known as the Squeezebox Touch (which looks like a 4.2 LED panel) or (slaver, slobber) a 4.2" or 5" eInk display - either mono or colour would do nicely.
I was really hinting that Sven might like to work on writing a driver that appears as a device file in a similar fashion to the serial drivers and that, like them, can be configured by a utility program that sets parameters in the device file.
-- martin@ | Martin Gregorie gregorie. | Essex, UK org |
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