LCD Reset Problem

I have come across the same problem on a variety of PIC processors with a variety of 4 line LCDs:

1. They always work OK on power-up.

2. If 're-set' only lines 1 and 3 display, 2 and 4 are blank. If one does multiple re-sets all four line occasionally work.

3. I have experimented with a variety of:
*Oscillator/Xtal speeds
*DEFINE LCD_COMMANDUS delays
*DEFINE LCD_DATAUS delays
*Various brown-out setting in the configuration word/s
*And nothing seems to make all four lines work on re-set

This is a fault that is difficult to pin down. Some systems never have this fault whilst others nearly always resuse to show lines 2 and 4.

I do have the appropriate DEFINES for the LCDs: D,E,RS,Lines,Bits

Any hints please?

Regards Bill Legge

Hi Bill,
Try FLAGS = 0 early in your code.

Joe S

Thanks very much, your tip worked

FLAGS=0 Did the trick.

I've looked up the note on FLAGS=0 in the LCDOUT command page of the PBP manual and don't understand how it works?

1. If I cycle the power to the PIC, without 'FLAGS=0' all is OK.
2. If I re-set I get the missing lines problem unless the statement 'FLAGS=0' is included.

I thought the PIC executed the same code on re-set as on power-up?

Whatever, you help is much appreciated.

Regards Bill Legge

Quote:

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Originally Posted by Bill Legge

Joe S

Thanks very much, your tip worked

FLAGS=0 Did the trick.

I've looked up the note on FLAGS=0 in the LCDOUT command page of the PBP manual and don't understand how it works?

1. If I cycle the power to the PIC, without 'FLAGS=0' all is OK.
2. If I re-set I get the missing lines problem unless the statement 'FLAGS=0' is included.

I thought the PIC executed the same code on re-set as on power-up?

Whatever, you help is much appreciated.

Regards Bill Legge

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It causes the LCD to reset each time the lcdout statement sends data to it.

little deeper.... when you clear FLAGS value, the next LCDOUT will include the whole LCD initialization commands (1 line or more, 4 or 8 bits mode etc etc... see your LCD datasheet), then send your data.

You can do it manually with few LCDOUT, but since FLAGS-0 do the job, why messing with it euh? ;)

Just curious Bill, "reset" used in the first post, what do you mean by that, are you taking the mclr line low or doing a full power off scenario?
I ask because a power off that only browns out the LCD may be the entire problem. There will be times you do not want to use flags = 0 due to latency problems.

Joe S

The boards I'm using have a 10k resistor that normally holds MCLR high. The re-set button takes the MCLR pin direct to ground. The power is on all the time.

I have been lazy with LCDs and not bothered with the spec sheets - just use the PBP LCD commands.

FLAGS=0 has solved most of my problems but I still get the odd occasion when alternate lines of the LCD don't come to life.

I suspect that the proper way to fix this is some combination of FLAGS and the configuration brown-out settings. AND READ THE SPEC SHEETS!

I mostly use PIC16F877A and PIC18F8722 chips on Mikroelektronika boards for developement and move to Futurlec boards for the end product - all hobby stuff, no production.

Thanks for you interest.

Regards Bill Legge