16F88 internal clock configuration

[Melanie]

There are many options here… so here‘s just one of them…

1. Ensure that your Device Oscillator Configuration Bits are set to INTRC_OSC_NOCLKOUT (if you don’t know how to do this, see the new FAQ section). This option also means that the two OSC pins are made available for I/O. If you need the Oscillator to output on OSC2, then select the appropriate option (again see FAQ section).

2. Somewhere at the start of your program (where you normally initialise your processors registers) add the line…

OSCCON=%01111000

I refer you to the Datasheet section 4, especially Register 4.2 OSCCON to discover what I have done.

3. If stabilising your clock to other events is important to you, then you may need to add this piece of code after the above OSCCON setting (otherwise it is not necessary)…

While OSCCON.2=0:Wend

This will ensure the PIC does not continue processing until the new Oscillator Frequency is stable by introducing a 4mS delay (see datasheet 4.6.5 item 4).

As with ALL the queries regarding the set-up of PICs – Read the Datasheet! – it’s all there waiting for you to discover.

[Tom Gonser]

As I am new to this, reading the data sheets sometimes pose more questions than they answer. Such is with trying to figure out how to use the Internal Osc on the 16F88.

I am moving from a 16876A where I used and external Osc - and have a program running fine there. Now, I want to move this program to the 16F88, and rather than use external Osc, use an internal. I have recompiled, tweaked the PORT.X settings, and am ready to go, BUT.

I see the F88 is an 8 mhz OSC, when I was using 4... Sure, I'd like to go faster, but just sticking to the same as the first pic is fine.

I have seen mention of setting the config bits to INTRC_OSC_NOCLKOUT in the include file.

As well I have seen advise to use OSCCON=%01111000 at the start - which mapping back to the data sheet looks like it is selecting a speed, but I can't find a table that maps to this..

I have also seen several references to OSC as RA6, etc... I just simply need to know what to read to find out how to use the internal oscillator and set it appropriately.. anyone have a few mintues to help out with a reply..

[mister_e]

Not quite sure as i didn't see any parts of your code but, if your 8MHZ setting is ok, you also must add DEFINE OSC 8 at the top.. did you?

for the internal setting, see datasheet in the OSCCON. all the setting are there.

in your case for 8MHZ
OSCCON=%01111000

for 4MHZ
OSCCON=%01101000

and so on for the other type of setting

[Tom Gonser]

Much closer.. THANKS!

I now see data on the LCD and on the 4800b Hyperterm screen, but the numbers are incorrect.. and the routines run differently..

Where data was reporting '1009', the text tag is fine, but the actual data is different..... like '3345', etc.

It looks like a timing problem some way?

Would the config bits effect this?

TG

[mister_e]

As we don't have any more info on your current project, it's still hard too see what's wrong with.. BUT at least, since your LCD and your serial communication are working without any kind of garbage display, it's a good sign that your PIC and code are running at the good speed.

If you did some assembler delay or something using TIMERs you must set your prescallers, rates, and delay with the new crystal speed

Did you try with the internal 4MHZ setting???

[Tom Gonser]

Hmmm.. I have tried with:

DEFINE OSC 4 'I want to use 4 mhz?
OSCCON=%01101000

and with setting these to 8Mhz ..

DEFINE OSC 8
OSCCON=%01111000 '8 Mhz

Both work about the same - 'some' plain text comes through, but the code is resetting because I am getting the initialization routine, which does not happen usually.

I am not doing any interrupts or anything, no jumps to assmbly code - pretty straightforward.

I did change the INC files:

changed the "XT_OSC" for "INTRC_OSC_NOCLKOUT" - It looks like this now:

;************************************************* ***************
;* 16F88.INC *
;* *
;* By : Leonard Zerman, Jeff Schmoyer *
;* Notice : Copyright (c) 2003 microEngineering Labs, Inc. *
;* All Rights Reserved *
;* Date : 08/13/03 *
;* Version : 2.45 beta *
;* Notes : *
;************************************************* ***************
; Modified by THG - changed clock settin from XT_OSC
NOLIST
ifdef PM_USED
LIST
include 'M16F88.INC' ; PM header
device pic16F88, INTRC_OSC_NOCLKOUT, wdt_on, pwrt_on, lvp_off, protect_off
XALL
NOLIST
else
LIST
LIST p = 16F88, r = dec, w = -302
INCLUDE "P16F88.INC" ; MPASM Header
__config _CONFIG1, INTRC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_ON & _LVP_OFF & _CP_OFF
NOLIST
endif
LIST

The strangest thing is that the program appears to be restarting when it should not. It should be looping through the main routine, but on the F88, it is picking up the initialization routine every few seconds.

scratching head....

[mister_e]

Hehe... i guess i found the problem

Here's all the configuration fuse available for you 16F88

;Configuration Byte 1 Options
_CP_ALL                      EQU     H'1FFF'
_CP_OFF	                     EQU     H'3FFF'
_CCP1_RB0		    		 EQU     H'3FFF'
_CCP1_RB3                    EQU     H'2FFF'
_DEBUG_OFF                   EQU     H'3FFF'
_DEBUG_ON                    EQU     H'37FF'
_WRT_PROTECT_OFF             EQU     H'3FFF'	;No program memory write protection
_WRT_PROTECT_256             EQU     H'3DFF'	;First 256 program memory protected
_WRT_PROTECT_2048            EQU     H'3BFF'	;First 2048 program memory protected
_WRT_PROTECT_ALL             EQU     H'39FF'	;All of program memory protected
_CPD_ON                      EQU     H'3EFF'
_CPD_OFF                     EQU     H'3FFF'
_LVP_ON                      EQU     H'3FFF'
_LVP_OFF                     EQU     H'3F7F'
_BODEN_ON                    EQU     H'3FFF'
_BODEN_OFF                   EQU     H'3FBF'
_MCLR_ON		   		     EQU     H'3FFF'
_MCLR_OFF                    EQU     H'3FDF'
_PWRTE_OFF                   EQU     H'3FFF'
_PWRTE_ON                    EQU     H'3FF7'
_WDT_ON                      EQU     H'3FFF'
_WDT_OFF                     EQU     H'3FFB'
_EXTRC_CLKOUT		    	 EQU     H'3FFF'
_EXTRC_IO		    		 EQU     H'3FFE'
_INTRC_CLKOUT                EQU     H'3FFD'
_INTRC_IO		    		 EQU     H'3FFC'
_EXTCLK			    		 EQU     H'3FEF'
_HS_OSC                      EQU     H'3FEE'
_XT_OSC                      EQU     H'3FED'
_LP_OSC                      EQU     H'3FEC'

;Configuration Byte 2 Options
_IESO_ON                     EQU     H'3FFF'
_IESO_OFF                    EQU     H'3FFD'
_FCMEN_ON                    EQU     H'3FFF'
_FCMEN_OFF                   EQU     H'3FFE'

use _INTRC_IO instead... i'm sure that will work.

[Kaya Onur]

There are many options here… so here‘s just one of them…

1. Ensure that your Device Oscillator Configuration Bits are set to INTRC_OSC_NOCLKOUT (if you don’t know how to do this, see the new FAQ section).

Hi everybody, I have just started to learn about pic programming. My searches through Google end up in this forum most of the time.

Could you please guide me to this FAQ section mentioned? I tried every FAQ link on the pages but I am unable to find the correct one which will take me to the place where this INTRC_OSC_NOCLKOUT and other options are explained.

Thanks.

[mackrackit]

I think this is what you are looking for
http://www.picbasic.co.uk/forum/showthread.php?t=543

[Kaya Onur]

I think this is what you are looking for
http://www.picbasic.co.uk/forum/showthread.php?t=543

It is! Thank you.