Ports won't display

[jasbertfalutine]

Hi everybody,
i have tried to write a simple program to display on led.
i used the template source and the linker script from microchip but i keep getting an error on stack underflow at address 0x00005 of my 16f877a chip

 

[mister_e]

how about posting the code?

 

[jasbertfalutine]

banksel trisb
movlw b'00000000'
movwf trisb

clrf wreg
clrf portb

start incf portb
goto start
end

 

[Nigel Goodwin]

Is that all? - that seems lacking in many of the required lines?, such as setting the config fuses, specifying the processor and include file etc.

Also, 'incf portb' isn't complete, and probably isn't a good choice anyway?.

 

[jasbertfalutine]

banksel trisb
movlw b'00000000'
movwf trisb

clrf wreg
clrf portb

start incf portb
goto start
end

 

[jasbertfalutine]

the #include list has been added by the template and the processor type has also be specified together with interrupt controls.

 

[jasbertfalutine]

the project built well with no errors but i wouldn't run under the simulator

 

[Nigel Goodwin]

I never use either MPLAB, or the simulator, I just use MPASMWIN, the assembler part of MPLAB - and test the programs on hardware.

But how about correcting the 'incf' line?.

 

[jasbertfalutine]

i went to microchip forum and i had a gist that maybe the linker script has some parameters not properly set

 

[jasbertfalutine]

what could i use instead of "incf portb" command

 

[Nigel Goodwin]

what could i use instead of "incf portb" command

You could try adding all the parameters to it?, what destination are you sending the result to?. I can't even remember what the default is?, but it's important to add the destination to the end of such commands - in this case ', f' so the answer is written back to the port.

However, in this case, the rapid 'read, modify, write' might be a problem?, and I would suggest incrementing a GPR instead, then moving it to the port.

 

[eblc1388]

banksel trisb
movlw b'00000000'
movwf trisb
                       ;<<< misssing banksel portb here
clrf wreg
clrf portb

start incf portb
goto start
end

Hate to tell you but you are still in bank1, whereas portb is in bank0.