LCD Wiring Configuration

jhwatts

I'm trying to wire this display on to my demo board but not having to much luck. Could somebody spell it out for me. noobe

http://www.datasheetarchive.com/JM204A-datasheet.html

I currently have LCD pins 1,2 ran to ground and +5, LCD pin 5 is tied to pin 0 in the propeller and pin 6 is tied to pin 1, LCD pin 15 and 16 are ran to ground and +5.

Toby Seckshund

There are two ways of talking to the LCDs, one is the full 8 bit way, and the other (usuall because of pin useage) is the 4 bit way. The 4 bit sort does a double swipe at the upper (D4..D7) bits only, some circuits show the lower bits left open an others show the tied low.

You do not state how the PIN3 is connected, the data sheet states that it is the PSU for the LCD. Usually it is the CONTRAST pin and is fed from a 10K pot(ish) from + to ground (usually the position is down towards the ground end).

jhwatts

I have tied pin 3 to the ground using a 10k resistor. Still no luck.

Cluso99

OK here is what I have found. This is a pretty standard connection and is most likely a Hitachi HD44780 compatible.

There is an object in obex (LCDDEMO) that works just fine. BUT you need to change the pins to 4,5&6 because that object is for a different display with E,RW,RS whereas the datasheet you have (and mine) is RS,RW,E. Note the backlight is 15&16 and is not required for testing. Pin 3 can be ground (via 10K should be fine) - It is usual to use a 10K pot between 1&2 with the wiper to 3 - I started a thread to discuss the way to connect the contrast (pin3) to the prop. PJAllen found a way using pwm and a single pin and no resistors. Likewise, we found a way (untried) to power the backlight from a few prop pins and series resistors. http://forums.parallax.com/showthread.php?130420-PWM-to-control-LED-brightness-amp-contrast&highlight=LCD+contrast+backlight

PJAllen

The datasheet you linked to shows a mech dwg with pin 1
on one end and pin 16 at the other, but there are only 15
pins/dots total shown.
Hope that yours has 16.

I have attached a wiring diagram, the minimal requirement
for "4-bit mode", based on your datasheet, though I added
another dot, to show 16.

[Is it the datasheet or am I having a stroke? Anyone else
smell toast burning?]

As I see it, DB4-7 require pull-downs;.

jhwatts

I got it. I opened up the LCD object and used the wiring config from it. It only displays characters on the top two rows of the display. Why is that?

caskaz

Hi PJ.
Major LCD's DB4-7 doesn't need pull-downs, and DB0-3 shoud be open.

If you use 74HC164, wires are 3.
This use 8bit mode.

Toby Seckshund

I have had some problems with older LCD unit when 3.3 Volts are used they all seem to like 5 Volts to the LCD module and yet 3.3 V should be TTL compatable. You are only writing to the LCD so no protection should be required.

Most LCDs only reset themselves on power up, You can force a reset through software by sending three lots of 03's (I think) with short delays between them. The delays are required as these modules are very slow in comparison to any micro controller.

I have a couple of non standard LCD modules that only use 14 pins, I hoped that it was just the backlights being always on but i haven't chanced it yet. They are LXC1625STY and have two resin blobs on the back. If anybody has some data ???

Cluso99

jhwatts: Originally I saw all 4 lines but then I did my own and only saw 2 lines until I fixed the mode. It is because the addressing of the screen is funny. See the HD44780 spec for detailed instructions.

Are you using 4 bit mode or 8 bit mode? I am using 8bit mode.

BEEP

How to use Intelligent LCDs

idbruce

jhwatts

JonnyMac did a tutorial on the HD44780, which gives the basic safe wiring for the LCD. In his tutorial, he includes a transistor for controlling a backlight, you may or not want to add this transistor. Here is the link to that SpinZone article. http://www.parallax.com/Portals/0/Downloads/docs/cols/nv/prop/col/nvp2.pdf

Additionally, MagIO2 has a nice LCD object in the OBEX for controlling the display, but you will have to look that one up.

Bruce

Martin_H

The four pin interface to an LCD consumes six microcontroller pins, but using a serial shift register lets you do it with only three pins. The programming is more complicated, but it can be wrapped in a library and made fairly easy to use. This approach is pretty common among Arduino users.

PJAllen

Hi caskaz - I disagree with all that, but you can
go your own way. Who constitutes "major" in this context
anyway?
Unused data input to GND certainly does no harm; pulling-down
data inputs keeps things in known states and that's how I roll.*
[I've been at this "stuff" quite a while.]

jhwatts - Which "the LCD object" do you refer?

* - This way nothing's indeterminate
and nobody has to remember or guess

caskaz

HD44780's datasheet recommend D0-3 to open with 4bit mode.
DB0-7 is pulled up to Vcc inside HD44780.

When DB0-3 connect to GND: If signal-line is long, connecting to GND is good way.(maybe needing resister)
If only write-mode, no problem.
But if read-mode, DB0-3's output may be short to GND under some status.

ViH-min for Input is 2.2V on HD44780's datasheet. So propeller's port can connect directly to LCD-module.
But some module(using HD44780) is not 2.2V.
My JHD164A's ViH-min is 0.7Vdd(3.5V). Now direct connect is OK.

I read HD44780U's datasheet again.
When Vcc is 2.7 to 4.5V, ViH-min is 0.7Vcc.
When Vcc is 4.5 to 5.5V, ViH-min is 2.2V.
When Vcc is different, electric&timing also is different.

PJAllen

0.7Vdd(3.5V) or Vdd - 0.7?
44780S = 5V, 44780U = 3V. Are these still made by Hitachi?

Even Parallax examples have been inconsistent in this matter.
Yes, all 8 are bi-directional, tri-state data bus (I/O.)

I'm always using these as 4-bit. If my example pulled-down
DB0-3, too, as is my inclination, I'd get "grief" for that.
Howbeit, they're "not used during 4-bit operation."

I'm not being critical of your position, I'm mindful of "n00bs" and
their propensity to get in over their head - and their aversion to
resistors.

jhwatts

Here is the lcd object I used to get the wiring configuration.

jhwatts

Any suggestions on how to wire this. I would like to use the same lcd.spin object. I'm assuming it will be the same as the LCD above except for the chip select pin.

PJAllen

It's an extension without a filename.
Fascinating.

wrightme

And it downloads and is viewable. Even more fascinating.

HollyMinkowski

I love using those cheap HD44780 lCD displays.

I wish they would use an RGB LED to backlight them though.
It would be cool to be able to use color effects with them.
They could have just one color wired to the normal pin for
compatibility and add two extra connections somewhere for
those that want more bling.