External osc defines

[Mugelpower]

Hi Insiders,

I´m trying to convince a Pic16F628A to work at 20MHz (yes it is a 20Mhz device) with an external canned oscillator

but i don´t get the right configs:

@config_EXTCLK_OSC

this shows no error when compiled but the setup doesn´t work

this is my simple testcode.

NEVER GOT ANY 20MHZ DEVICE WORKING!!!! only 10MHz or below.

'************************************************* *******************************************
' 16F628A 4 Mhz crystal
' damn program should blink an LED every time a pulse goes into RB.0
' later a value should be serial loaded and set a delay before the blink pulse
'************************************************* *******************************************

'
' DEFINITIONS


@config_EXTCLK_OSC


CMCON=%00000111
led var portb.7



' START OF MAIN PROGRAM
'
CMCON = 7 ' RA0-RA3 are digital I/O
TRISA = 0 ' PORT A is output
TRISB = 1 ' RB0 is Input others output



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


END ' End of program

[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?