piclist 1998\10\07\231000a >
Thread: LCD Problem
face BY : Heinz Czychun email (remove spam text)

Hi Sean,

I also bought the same display, and also the 16x1. Assuming it to be a
standard type, I just connected it according to David Benson's Book PIC'n
up the Pace. The book provides a fairly complete treatment of these
displays, both 16x1, and 16x2 in a very understandable form, with complete
PIC software code.

At 6:24 PM 10/7/98, Sean Breheny wrote:
>Hi all,

...large snip...

>For example, there is an input signal/voltage
>listed as "Vo" on the pinout, and listed as an input on the block diagram,
>but it is mentioned nowhere else. The absolute maximum ratings only mention
>two supplies, Vdd and Vlcd, both of which should be 5V. Now, here's the
>second thing I don't understand: there are actually two terminals for Vlcd,
>positive and negative. Why two? Why wouldn't it just be referenced to Vss?
>Especially because its maximum input rating is given in terms of Vdd

from the book the pins from left to right ( with the display facing you) are

1 - GND
2 - +5V
3 - Gnd  -> voltage for display contrast (I've seen a 2k5 ohm voltage
divider for contrast but not tried it.)
4 - RS
5 - R/-W -> Grounded for most apps
6 - E    -> Positive logic (125 micro sec pulse)
7 - D0
8 - D1
9 - D2
10 - D3
11 - D4
12 - D5
13 - D6
14 - D7
15 - Not used   |
16 - Not used   |
               | I've taken these to be involved with backlighted displays
"+" - Not used  |
"-" - Not used  |

>There are also two additional solder pads on the side of the LCD board,
>marked + and -, which are never mentioned in the datasheet. The "-" one is
>connected internally to Vlcd(-), but the "+" one is not connected to either
>Vdd, Vss, or Vlcd(+).

This maybe for the backlight option ?

>This is a parallel interface LCD and I have code running on a PIC to send
>the correct data, at least according to the datasheet. The result is that I
>see nothing at all on the LCD screen. Nothing turns opaque.

Is pin 3 low?

>The datasheet
>is also not clear about whether or not the Enable signal is active high or
>low. It appears that a high-low transistion causes a load of the data, but
>it shows it in the low state before the data transfer, it goes high before
>the data is valid, drops to low while the data is valid, and goes back high
>at the end of the transfer,so it is not clear to me what value it should
>assume during idle
>I have tried treating the E as both active high and active low.

See above


>I guess the next step would be to try reading back what I have written to
>the display memory, to see if at least the LSI is running. However, I am
>hesitant to write extra code if there is a simple solution.

There are some tricks to allow the display time to initialize after powerup.
>One last note: The datasheet is for model MC162-1, but the board itself
>actually says MCC162A4-5. I hope that they are compatible <G>.





See also: www.piclist.com/techref/lcds.htm?key=lcd
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