External osc defines

[Archangel]

Try this:

@ __CONFIG_EXTCLK_OSC
DEFINE OSC 20

[Bruce]

Make sure you call-out all config options you need in the config directive line. Otherwise
they default to options you may not be aware of that can stop you dead in your tracks.

/MCLR is by default reset, and LVP is by default on. If you only indclude _EXTCLK_OSC, then
LVP is enabled, and can really screw things up.

Give this a shot.

  @ __config _EXTCLK_OSC & _WDT_OFF & _MCLRE_OFF & _LVP_OFF & _CP_OFF
  
  DEFINE OSC 20 
  LED VAR PORTB.7
  CMCON = 7 ' RA0-RA3 are digital I/O
  PORTB = %01111111 ' set port latches
  TRISB = %01111111 ' RB7 is output, rest are inputs.

main:
  led = 1
  pause 500
  led = 0
  pause 500
  goto main

  END ' End of program

[Mugelpower]

Hi Bruce,

I tried your Program but it gave me a compilation error I didn´t understand something like out of memory.

I tried Joes Define instead which at least showed no compilation error.

My small setup sits on a veroboard and I tried to hold all Cu-lines as short as possible and used the some capacitors etc.

99% of the time it didn´t work but some seconds the Led blinked as expected.

Tried some other 20Mhz 16F628A but they showed all the same behavior. Scope said the canned Oscillator is ok,. tried to use different resistors in line, parallel , from +5V to signal because it could have an open collector output......

In the evening I try again with a crystal. Damned!

[Bruce]

To use this config directive you need to use the MPASM assembler, and comment out any
MPASM config statments in the default PBP device header file.

If you're using the PM assembler, then change it to;

@ DEVICE EXTCLK_OSC, WDT_OFF, MCLR_OFF, LVP_OFF, PROTECT_OFF

If you're still having trouble see this thread http://www.picbasic.co.uk/forum/showthread.php?t=543

[Mugelpower]

Hi Bruce,

I´m using Micrchips MPASM and PBP 2.50

Did you use 20 MHz on a veroboard?

[Bruce]

I have never used vero board or a 20MHz canned type TTL clock oscillator, but I do use
20MHz crystals & resonators on breadboards pretty often.

What is the error you're seeing when you compile? The example I posted compiles fine here!

Edit: Which PIC are you compiling for? There are differences in config options between some
device types.

[Mugelpower]

Hi Guys!

This works:

'************************************************* *******************************************
' 16F628A 20Mhz extern canned Oscillator
' damn program should blink an LED
' Yeah Works!
'************************************************* *******************************************

@config_EXTCLK_OSC


DEFINE OSC 20
LED VAR PORTB.7
CMCON = 7 ' RA0-RA3 are digital I/O

TRISB = %01111111 ' RB7 is output, rest are inputs.

main:
led = 1
pause 500
led = 0
pause 500
goto main

END ' End of program

And heres the mistake:
http://hobby_elec.piclist.com/e_pic8_8.htm

Look at the osc wiring diagram: ext osc MUST be connected to RA6! hahahaha!