RA5 on PIC 16F627

[northsea]

Hi all,

I am creating my first application using a PIC. I have used all of the pins on the 16F627 and so need to use RA5. However I can't get it to act as an input. I have used the following lines to configure the comparators:

MOVLW B'00000111'
MOVWF CMCON

and I have added the following to the __CONFIG line:

_MCLRE_OFF

I have tried the same bit of circuit on a different input line and it works so I know it is not he external circuitry.

I have tied the RA5 pin to +5V using a 330K resistor and then use a switch to ground (as I have done with the other working inputs).

The program appears to read the pin as a zero and when I press the switch resets the micro.

Any ideas would be greatly appreciated.

 

[blueroomelectronics]

Depending on the programmer you're using you may put the 16F627 in a non reflashable mode from using MCLR as an input. Make sure your programmer supports VPP before VDD.

330K is very high for a pullup, try 33K

 

[Nigel Goodwin]

The program appears to read the pin as a zero and when I press the switch resets the micro.

Any ideas would be greatly appreciated.

Fairly obviously, as pressing the switch generates a reset, MCLR is still being used as a reset pin - and not not an I/O pin - so you're not setting the fuses correctly.

 

[northsea]

Thanks for your responses.

I ammended the __CONFIG line to _MCLRE_OFF. Are there any other fuses I should be setting?

I am using a Velleman programmer and then removing the chip to test it in my own circuit.

 

[Nigel Goodwin]

Doesn't your programmer software show the fuse settings when you load the HEX file? - presumably you're using a 627 and not a 627A?.

 

[northsea]

No it doesn't show the fuse settings when you load the HEX file. It's just a simple thing that came with the Velleman kit. I am just using notepad to write the assembler.

 

[Nigel Goodwin]

Is your chip a 627 or a 627A?.

 

[northsea]

Sorry, it's a 627

 

[Nigel Goodwin]

Show your complete config line!.

 

[northsea]

__config _boden_on & _cp_off & _data_cp_off & _pwrte_on & _wdt_off & _lvp_off & _mclre_off & _xt_osc

 

[Nigel Goodwin]

Try __CONFIG 0x3D41 instead.

I'm presuming your programmer software supports the 16F627?.

 

[northsea]

OK. Got to go out now but will try first thing tomorrow. Thanks a lot for your time.

 

[northsea]

Hello again,

After a few attempts I realised that the programmer wasn't updating the config word. 0x3F41 works fine now. Thanks a lot for all your help.

 

[blueroomelectronics]

The Velleman K8048 is not a VPP before VDD programmer, you may have a tough time reprogamming the 16F627 if the internal osc and MCLR are both internal.
https://www.electronics-lab.com/forum/index.php?topic=12293.0;wap2

 

[Pommie]

Hello again,

After a few attempts I realised that the programmer wasn't updating the config word. 0x3F41 works fine now. Thanks a lot for all your help.

How can that be?

The two config statements produce exactly the same hex file. Can someone explain this????

Mike.

 

[blueroomelectronics]

The programming software may mask off bits it considers in confilict with its capabilities.
MPLAB enable/disables the DEBUG_ON bit by itself when needed.

 

[northsea]

How can that be?

The two config statements produce exactly the same hex file. Can someone explain this????

Mike.

Yes, the config lines are the same. It wasn't the config line that was the problem - it just appeared that the Velleman programmer wasn't updating the PIC after I made changes even thought the "update config word" box was ticked. I loaded the HEX file again and it worked.

Thanks for your interest.