hi Big,
This short clip shows result for your posted asm file.

Remove .txt extension to view the .mp4

E

 

There are four common issues with trying to get 1602 displays to work.

1) Adjusting and setting the contrast voltage properly.
2) Initializing the LCD.
3) Proper time delays when sending control signals.
4) Proper power supply decoupling.

Start by attempting to display a single character such as ’A’ or ‘0’.
The next step would be display a sequence of characters using an iterative loop.

For example, ’0’ to ‘9’.
‘0’ is 48 or 0x30.
Iterate ten times, incrementing the output register at each iteration.

If that works, try 16 characters from ‘A’ to ’P’.

MrChips,

1) on initlal power up I send to the display 'PLEASE WAIT' which it displays reliably and regularly. The reason for this is on power up they will have to wait for a minute to count the revolutions per minute.
This rules out incorrect settings of the contrast voltage.
2) as above means the displaay is initialized correctly.
3) the delay called is approx. 2mS which far exceeds the minimum requirements, their is no maximum.
4) the unit is powered from a 12v battery with a LM7805 on board with a .22uF on the input and a 0.1uF on the output. Properly not necessary but I done it just in case.

'For example, ’0’ to ‘9’.
‘0’ is 48 or 0x30.
Iterate ten times, incrementing the output register at each iteration.'

I did that and it displayed 0 to 7 but not 8 or 9, it's repeatable so it not random but something to do with 8 and or 9.
This is really weird - i sent the Ascii code for 8 after PLEASE WAIT expecting to see PLEASE WAIT8. PLEASE WAIT displayed briefly but when it hit 8 the display went blank. I thought the only way to clear the display was to send the Clear Display command.

 

Ok. Skip the startup “PLEASE WAIT”.

Simply send “8” repeatedly with about 1-second delay after each send.

 

Ok. Skip the startup “PLEASE WAIT”.

Simply send “8” repeatedly with about 1-second delay after each send.

Ok done as above and the display stayed blank. I substituted "8" for "0" and it quite happily displayed 0 approx. every second.

 

Ok done as above and the display stayed blank. I substituted "8" for "0" and it quite happily displayed 0 approx. every second.

Please post the code you used for displaying “8”.

 

Please post the code you used for displaying “8”.

MrChips - please find attached.
Are you familiar with the Microchip Assembler MPASM?
If so you will know that any Alphanumeric characters in '' the Assembler converts to Ascii.

 

MrChips - please find attached.
Are you familiar with the Microchip Assembler MPASM?
If so you will know that any Alphanumeric characters in '' the Assembler converts to Ascii.

Instead of
MOVLW ‘8’

use
MOVLW 56

 

Instead of
MOVLW ‘8’

use
MOVLW 56

I've already tried that, even tried 38hex and binary 00111000, all produce the same affect.

 

I've already tried that, even tried 38hex and binary 00111000, all produce the same affect.

Ok.
Can you post a photo of your setup?
We would like to see the wiring between the PIC MCU and the LCD.

The next step is to put a 0.1 μF ceramic capacitor across pins 1 and 2 at the LCD, not on the Vero board but on the LCD itself.

Edit: And if that doesn’t fix the problem, try a 10 μF electrolytic capacitor next.

 

Ok.
Can you post a photo of your setup?
We would like to see the wiring between the PIC MCU and the LCD.

The next step is to put a 0.1 μF ceramic capacitor across pins 1 and 2 at the LCD itself.

Attached is the photo, it's not very good quality as my digital camera does not focus to good for close ups.

The build is not up to my usual standard as the Windmill Trust hasn't got a lot of money. If no expense spared I would have bought some new stripboard but, in order to keep the cost down, I used some old stripboard from a redundant project.

I will add the 100nF cap. tomorrow.

 

Hi Big,
One common cause of PCB short circuits is when using the spot faced cutter to remove copper between holes.
A thin sliver of uncut copper can cause a short, check the cut holes.
E

 

Ok.
Can you post a photo of your setup?
We would like to see the wiring between the PIC MCU and the LCD.

The next step is to put a 0.1 μF ceramic capacitor across pins 1 and 2 at the LCD, not on the Vero board but on the LCD itself.

Edit: And if that doesn’t fix the problem, try a 10 μF electrolytic capacitor next.

I tried an 0.1 μF cap. but didn't have a 10 μF cap. to hand so used a 47 μF, unfortunately neither fixed the problem.

 

I tried an 0.1 μF cap. but didn't have a 10 μF cap. to hand so used a 47 μF, unfortunately neither fixed the problem.

We are running out of possible things to try.

One last thing I can suggest is, there is E signal that is sent after the data is sent. Try lengthening the delay between the data and E.

I will have a look at your code a bit later today.

 

In your SEND2LCD subroutine, you have E signal inverted.

Use:

BSF PORTA, RA1
CALL DELAY_3
BCF PORTA, RA1

Remove the first instruction
BSF PORTA, RA1

 

In your SEND2LCD subroutine, you have E signal inverted.

Use:

BSF PORTA, RA1
CALL DELAY_3
BCF PORTA, RA1

Remove the first instruction
BSF PORTA, RA1

MrChips, I'm confused as to the changes you want me to make, would you kindly post SEND2LCD with your changes incorporated.

I'm trying to learn how to use the Special Characters function but the datasheet doesn't provide much information. My thoughts are if I generate an 8 as a special character will it then display it.

 

;this routine sends data/commands to display
;NOTE - RS (RA0 bit 0) must be set to data or command
;        prior to using this routine.
SEND2LCD   
            BCF     PORTA,RA1          ; this line can be eliminated if already done at initialization

            MOVWF    PORTB
            CALL    DELAY_3
            BSF      PORTA,RA1            ;LATCH IN DATA
            CALL    DELAY_3
            BCF      PORTA,RA1            ;FOR NEXT TRANSMISSION
            RETURN

 

;this routine sends data/commands to display
;NOTE - RS (RA0 bit 0) must be set to data or command
;        prior to using this routine.
SEND2LCD  
            BCF     PORTA,RA1          ; this line can be eliminated if already done at initialization

            MOVWF    PORTB
            CALL    DELAY_3
            BSF      PORTA,RA1            ;LATCH IN DATA
            CALL    DELAY_3
            BCF      PORTA,RA1            ;FOR NEXT TRANSMISSION
            RETURN

That didn't work MrChips, in fact it didn't even initialise the LCD let alone display please wait.
I substituted the original SEND2LCD and that worked, well at least it displayed please wait.
I guess my only hope is to find out how to use Custom Characters, generate an 8 and hope it displayes.

 

That didn't work MrChips, in fact it didn't even initialise the LCD let alone display please wait.
I substituted the original SEND2LCD and that worked, well at least it displayed please wait.
I guess my only hope is to find out how to use Custom Characters, generate an 8 and hope it displayes.

No. The problem is not resolved by using Custom Characters.
The problem is with how your control signal E is being generated.
There is something wrong that I cannot see from where I am sitting.
If I were there with an oscilloscope I would get a clearer picture.

Do you have access to an oscilloscope?

 

Your problem could be the:

dreaded PIC RMW problem

This is a real problem, you should never use instructions like BSF or BCF to the PIC PORT registers.

 

Ah, yes. One of the many reasons I don’t do PICs.