Oscillator/Hserout woes

[HankMcSpank]

Need a sanity check here!

I've been runing on an external 20Mhz resonator ....HSEROUT worked fine.

now want to go with the PIC's 4Mhz internal oscillator (to free up a couple of pins)...but no matter what I do, HSEROUT is garbage.

I'm using MPASM... the16F690inc file has a couple of options that I'm not clear about...

_INTRC_OSC_NOCLKOUT
_INTOSC

...could someone tell me why two options that look similar? (I've tried both....but sticking with _INTRC_OSC_NOCLKOUT )

Anyway, back to my problem....

@ __CONFIG _FCMEN_OFF & _INTRC_OSC_NOCLKOUT & _WDT_OFF & _MCLRE_OFF & _CP_OFF & _IESO_OFF & _BOR_OFF & _PWRTE_OFF

DEFINE  OSC 4          ' set Oscillator at 4Mhz.

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 20h ' Enable transmit, BRGH = 0
DEFINE HSER_CLROERR 1 ' Clear overflow automatically
DEFINE HSER_SPBRG 25  ' 9600 Baud @ 4MHz, 0.16%
SPBRGH = 0
BAUDCTL.3 = 1         ' Enable 16 bit baudrate generator



Include "modedefs.bas"

ANSELH=0
ANSEL=0
CM1CON0 =0
CM2CON0 =0
CM2CON1 =0
adcon1=0
TRISB.6 = 1
TRISB.7 = 0
TRISC=%00000000 ; set all Port C pins as outputs
rcsta.7=1 'SPEN serial port enable bi


loop1: 
hserout ["hello", 13, 10]
pause 250
goto loop1
end

Grateful for any input here....I'm going crazy looking at this problem for hours!

Edit: Just rolled back to the external 20Mhz resonator oscillator - Hserout works just fine - could it be the internal oscillator is out of spec & therefore wrong after being divided down?

[HenrikOlsson]

Hi Hank,
Have you verified that the PIC is running at 4Mhz? Toggle a LED at 1Hz or something will show you that if it's 4Mhz (which if I'm not mistaken is the default for the internal oscialltor) or if it's something else.

Have you tried to simply DEFINE HSER_BAUD 9600 ?

Next, have you tried another baudrate, say 2400baud? The specs says that internal oscilaltor is off by no more than +/-1%. I'm not sure what's tolarable when it comes to RS232 but lowering the generated baudrate will lower any fault introduced by the oscillator - worth a try.

Finally, the internal oscillator can be setup to either output the clocksignal on the OSC/CLKOUT pin on a pin or not - that's the two options.

/Henrik.

[ScaleRobotics]

You should set the OSCCON register in your code. There are a lot of speed options for your chip, from 8mhz to 32khz. Looks like it defaults to 8mhz if left untouched.

[HankMcSpank]

You should set the OSCCON register in your code. There are a lot of speed options for your chip, from 8mhz to 32khz. Looks like it defaults to 8mhz if left untouched.

Thanks for the input guys

As it goes (out of desperation), I tried a few permutations of OSCCON prior to posting (but wasn't too sure whether the OSCCON setting overode the define command or not)

I have to say all the config setting surrounding something as elementary as setting an oscillator up is very confusing!

So having got the fuse correct ( _INTRC_OSC_NOCLKOUT ...at least that's what's in the 16f690.inc MPSAM file)

Having got the define correct. (define osc 4 ....4Mhz)

The OSCCON still needs setting? (bear with me here - I seldom change this stuff.....if OSCCON still needs setting what's the purpose of the DEFINE command?)

I tried getting the interal oscillator presented on the associated IO pins (to see if I could scope them - failed! IS there something unique about the clock that makes it invisible? lol)

I tried a whole heap of permutations - the Hserout settings I posted were derived from Mr E's calculator.

The weird things is ...when on internal oscialltor, most of the 'format' of the text onscreen was almost there (eg tabs were in the right places, therefore forming columns as the lines wrapped ...just gobbledegook when on the internal oscillator). I'll come back to this later, but for the time being I'll stick with 20Mhz!

Incidentally, when I scope the PICs OSC pins when using an external resonator - I can't scope the signal either ....I'm starting to think this is personal & that the clock oscillator from just me!!!!! (not saying I'm paranoid - I used to play rugby but gave up becuase everytime there was a scrum, I thought they were talking about me)

[ScaleRobotics]

Having got the define correct. (define osc 4 ....4Mhz)

The OSCCON still needs setting? (bear with me here - I seldom change this stuff.....if OSCCON still needs setting what's the purpose of the DEFINE command?)

I tried getting the interal oscillator presented on the associated IO pins (to see if I could scop them - failed! IS there something unique about the clock that makes it invisible? lol)

I tried a whole heap of permutations - the Hserout settings I posted were derived from Mr E's calculator.

No, you were correct, it defaults to 4 mhz, and should not need to be set, unless you want to try 8 mhz. Which, maybe you should, just for fun. But try what Henrik suggested with verifying your osc speed by toggling an led, and see what you get, just to be sure.

[HenrikOlsson]

Hi,
DEFINE OSC 4 doesn't do anything with the PICs registers or config "fuses". It simply tells the compiler that you are intending to run the chip at 4Mhz so it knows how to calculate the correct amount of cycles for your PAUSE 250 etc.

The internal oscillator on the '690 is fixed* at 8Mhz but the postscaler (controlled by bits 4, 5 and 6 in the OSCCON register) defaults to a divide by 2 ratio so you end up with 4Mhz as the default. So really, it should be running at 4Mhz.

* The "fixed" 8Mhz oscillator can be tuned by changing the OSCTUNE register.

When you tried to get the CLKOUT to work, did you set the pin to output? (TRISA.4 = 0)

/Henrik.

EDIT: Running at 4Mhz you should see a 1Mhz signal on the CLKOUT pin.

[HankMcSpank]

Hi,
DEFINE OSC 4 doesn't do anything with the PICs registers or config "fuses". It simply tells the compiler that you are intending to run the chip at 4Mhz so it knows how to calculate the correct amount of cycles for your PAUSE 250 etc.

The internal oscillator on the '690 is fixed* at 8Mhz but the postscaler (controlled by bits 4, 5 and 6 in the OSCCON register) defaults to a divide by 2 ratio so you end up with 4Mhz as the default. So really, it should be running at 4Mhz.

* The "fixed" 8Mhz oscillator can be tuned by changing the OSCTUNE register.

When you tried to get the CLKOUT to work, did you set the pin to output? (TRISA.4 = 0)

/Henrik.

EDIT: Running at 4Mhz you should see a 1Mhz signal on the CLKOUT pin.

Great stuff Henrik - like I say, in the end I went back to 20Mhz (& all the associated pin rejigging that entails from having to put back in the an external resonator!)...I don't have the heart or inner strength to now 'rejg' my 'rejig' so to speak ......but I *will* revisit this with the advice/knowledge gained here (I'd dearly love to see some form of clock coming out of the pesky pins - if for no other reason to establish that the PIC isn't holding a grudge against me!)

A hearty thanks!

[ScaleRobotics]

Sorry, it does default to 4mhz, I can't read binary until I have my coffee ... sorry.