8x8 dot Matrix not displaying proper message

[temtronic]

It appears that 2 columns are not working not 'some dots' ?

Easy to debug...
First, get rid of all wiring except for the LED display, a resistor and power supply. Play 'computer' and test each row and column combination to verify that the LED module is 100% working. Should take you 10 minutes.

Second, rewire your PIC and parts back up and retest using a 'one LED on' program. Using a simple 'for loop, select LED, delay 1 second' program will 'cycle' all the LED dots.

Third, my hunch is you have NOT disabled some onboard peripheral that is defaulted to control 2 'column' I/O pins.

Fourth, or....you've blown up those pins ! A simple LED-resistor test will confirm this.

It all gets down to basic trouble shooting, start with a known condition and proceed in a logical pattern AFTER you confirm the hardware is 100% working. Also be sure to recheck your wiring..it's real easy to mis-count a pin or plug the 'red' wire where the green one goes.....

hth
jay

[ezflyr]

Hi,

Is this a 'real' hardware project? If so, would you kindly snap a picture so
that we can see how you have things wired up?

John

[Mike Walne]

OK you've changed your schematic.

Part of your circuit now looks like this:-

[Mike Walne]

OK. I've had time to burn your code (not mine) into a PIC16F877, I don't have the 'A' version.
I've had a look with a 'scope.

You've studiously ignored my previous questions about power and 'scopes.

So here goes:-

There does not appear to be anything stuck.
All the PORTD pins waggle up and down in the correct sequence.
All the drives to the '595 operate.
There are groups of 8 pulses on the CLOCK line.
There's activity on the DATA line.
And single pulses on the control lines.

I don't have '595s so can't test that bit.
I have read the data sheet, and suspect it should be working (after a fashion).

Like others have suggested, it looks like you've got a connection problem, or something is stuffed.
Serious testing/debugging called for.

Your operating sequence is wrong.

You're updating the '595 outputs THEN changing the PORTD.

The effect is that you'll get ghosting between LED columns.

Also you're wasting time.

You don't need to reset the '595 outputs.
You could, instead, feed data into its serial register as a background task.

At this stage the ghosting and the time issues may not be important, but they will be if you ever get the stage of driving a larger display.

Mike

EDIT What you're doing is even worse than I realised at first glance.

After the '595 reset, ALL the LEDs of the current column will be turned ON.
They remain ON 'til the following data latch pulse.

The LEDs in the next column also light briefly in the wrong column.

Like I said before, you MUST turn OFF ALL the anodes whilst updating the cathodes.

Bear in mind, I don't have your hardware in front of me, nor do I have '595s to test, so there are other possible problems I have not noticed.

[Mike Walne]

You may ask, why am I being paranoid about one PIC port sourcing/sinking 80mA.

Quite simply, the manufacturer of your 8x8 matrix more than likely went to the trouble af matching the LEDs.
You're doing your best to defeat that.
For any column with all 8 LEDs ON, the PIC will struggle to handle enough current.
On the other hand driving a column with only one LED ON will be easy.
The visual effect will be that the one LED will be significantly brighter than each of those in the fully lit column.
The display will look odd.

I, for one, would not be happy.

You need to follow temtronic and other's advice regarding testing debugging etc.

The following code will exercise everything for you.
It activates each column in turn.
Whilst one column is active it lights one LED in that column in turn.
So you should see ALL the LEDs light (fairly dim, but equally lit).
You can probe ALL the column and row drivers with a 'scope.
This code should allow you to probe both the PIC and the '595, i.e. everything.
WHEN you know that everything's working THEN proceed with YOUR coding.

[kein]

Gents,
Sorry, I have been out of the scene recovering. I can't thank you enough for your comments, direction and help. I will put them into action between today and tomorrow and will post a response.
Once again thanks for sharing hard earned experiential knowledge with me.
Long live knowledge!