Post by thread:LCD help.

I have a standard 2 line Hitachi 44780 controlled display that is not working and I need some suggestions for further debugging steps. It has the standard 14 pin header and I have it wired up for 4 bit mode using a 74HC164 shift register like the example in Myke Predko's "Programming and Customizing the PIC" book. I am using his LCD 3 line code as well. Power is supplied by 4 AA batteries measuring 5.16 volts. The PIC is a 16C84 and the connections are as follows: RB5 - data out to shift register A&B inputs (tied together) RB6 - clock out to shift register clock RB7 - to LCD enable line Vcc - to common +5v Gnd - to common gnd On the 74HC164 the connections are: A&B data inputs - from PIC Q0 - LCD line 11 - DB4 Q1 - LCD line 12 - DB5 Q2 - LCD line 13 - DB6 Q3 - LCD line 14 - DB7 Q4 - LCD R/S MR - tied to VCC Vcc - to common +5v Gnd - to common gnd The other relevant lines on the LCD are the R/W line which is tied to ground, and the contrast adjustment. For contrast adjustment I have a 20k potentiometer wired as a voltage divider with the center tap connecting to pin 3 on the LCD. I have verified all the normal things, my PIC is running, the shift register is shifting, the LCD is getting power and signals on the data lines. But the display remains blank. Do I need to provide some form of external oscillation for the LCD? Do I need to provide the 5 different voltage levels as per the 44780 datasheet? Is there some way to test the LCD to see if it is good? (I got it secondhand from a friend so I have no idea about its past life). Do I need to do something with the 4 unused data lines or can I just leave them unconnected? Any ideas on where to look next are greatly appreciated. TIA, Adam

> I have verified all the normal things, my PIC is running, the shift > register is shifting, the LCD is getting power and signals on the data > lines. But the display remains blank. > > Do I need to provide some form of external oscillation for the LCD? No > Do I need to provide the 5 different voltage levels as per the 44780 datasheet ? No > Is there some way to test the LCD to see if it is good? (I got it > secondhand from a friend so I have no idea about its past life). Get your code working.. :) > Do I need > to do something with the 4 unused data lines or can I just leave them > unconnected? Float is fine. Does the code set 4 bit mode? Does the code test the busy bit? You should have E, RS and R/W.. If you tie RS(MR?) high, then you can only send data to the LCD, never commands. This means that you are relying on the internal reset in the display, which is a maybe thing.. I would bring RS back to the processor, and do the wakeup handshake dance. You need a datasheet most heinously..

On Wed, 11 Nov 1998 09:21:33 -0700 Adam Bryant <spam_OUTadam_bryantTakeThisOuTEMAIL.MOORE.COM> writes: >I have verified all the normal things, my PIC is running, the shift >register is shifting, the LCD is getting power and signals on the data >lines. But the display remains blank. If you just turn the power on without sending any commands, the LCD should come up in the one-line x8 mode displaying all blanks. Turning the contrast voltage up somewhat past the normal operating point should cause the first line to go all dark, while the second line if there is one stays off. If you can't get that to happen, either there is something wrong with the module or it is one of the extended temperature ones with different fluid in the LCD. These require a higher LCD voltage, and since the LCD voltage is between Vdd and Vlcd, the Vlcd pin needs to be taken negative (maybe 5V or more) to see anything. ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]

In a message dated 11/11/98 21:23:30 GMT, you write: << RB5 - data out to shift register A&B inputs (tied together) RB6 - clock out to shift register clock RB7 - to LCD enable line Vcc - to common +5v Gnd >> Try the Vo pin it needs about 0.7v (10k res to 5v 10k pot to 0v) to set the contrast.. remenber to ground the r/w pin dont leave floating Cheers Steve.....