PIC16F84A EEPROM problems

[The Master]

How about a little something, like a .1uf across Vdd and Vss on the PIC itself?

hmm, do i really need that? the origional diagram i had a few years back shows 1 there but i tried removing it and it didnt appear to affect anything.

ill try and find one. its not something i have laying around :P

[mister_e]

Try..

        @   __CONFIG _XT_OSC & _WDT_OFF & _CP_OFF
        
        PORTB = 0
        TRISB = 0
        
        DATA 0,1,2,4,8,16,32,64,128
        
        Addr var byte
        
        for Addr=0 to 8
            read Addr, PORTB
            PAUSE 500
            NEXT
            
        STOP

and make sure you have MCLR pin tied to VCC via a resistor. Cap always have to be there. 0.1, 0.22, 0.47 or whatever else in that range.

[The Master]

ok, i copied that exactly. it wouldnt compile because of the top line so i removed it and set the fuses in the programmer software. i borrowed one of those caps from another circuit and its still not working. im getting the exact same result

Edit: MCLR is connected to vdd with a 10K resistor

[mister_e]

OK, so what happen if you change the loop to

        for Addr=0 to 7
            PORTB = DCD ADDR
            PAUSE 500
            NEXT

If it doesn't work... or you have a faulty crystal, or your crystal capacitor are bad, or the PSU is bad, or the PIC is bad... OR everything previously listed

EDIT: config fuses..
http://www.picbasic.co.uk/forum/showthread.php?t=543

[The Master]

[QUOTE=mister_e;39699]OK, so what happen if you change the loop to

        for Addr=0 to 7
            PORTB = DCD ADDR
            PAUSE 500
            NEXT

that works. the LEDs are chasing as expected. what does this mean then?

[mister_e]

Probably the PIC EEPROM is bad OR there's a setting in your device programmer software that you overlooked.

What i mean is that some Device programmer software allow to program OR NOT the PIC EEPROM. Sure it's something like that.

[The Master]

Probably the PIC EEPROM is bad OR there's a setting in your device programmer software that you overlooked.

What i mean is that some Device programmer software allow to program OR NOT the PIC EEPROM. Sure it's something like that.

right. ive just tested it on another chip so its not that. theres 1 more fuse value you didnt mention so i changed that. the programmer app has an EEPROM override button so i tried that too and still as before.

this is confusing. random thought, could this possibly be anything like those chips where you have to access the *internal* EEPROM asif it was *external*?

another thing is that the datasheet for this chip says EEPROM stuff has to be written in a certain way but it only gives examples of assembly code so i dont understand it

[skimask]

hmm, do i really need that? the origional diagram i had a few years back shows 1 there but i tried removing it and it didnt appear to affect anything.

ill try and find one. its not something i have laying around :P

That was then, this is now... Just bad design practice NOT to use one, I don't think you'll find anybody who will dispute that fact. Just because it worked once, doesn't mean it'll work like that every time...however, conversely, you'll have a hard time finding a PIC that won't run because one is installed (vs. one without a cap installed).