What am I doing wrong ?

[malc-c]

I have the need to pulsate an LED rather than just turn it on or off. I've modified the code I used for my model train detection project that used a 16F628A and have a working example on my bread board. Although its not rocket science I used the PWM command and a for next loop to increase the on time of the LED and thus its brighness. However given that this is just my second project with PBP I'm well chuffed that it worked with very few attempts.

However, I really want to use a 12F675 so I copied and pasted the code, substituting PORTB.4 for GPIO.0 and compiled the code once the chip was selected in Microcode IDE. However it fails to work with the 12F675. Ive included the setting to make ports digital (I think) but it still fails, and I would really like some guidance here.

This is the code for the 12F675

GPIO.0 = 0
CMCON = 7 ' PortA Digital inputs
VRCON = 0        ' Voltage reference disabled
OPTION_REG.7 =    0


@RC_OSC_NOCLKOUT 
@WDT_ON
@PWRT_ON
@MCLR_OFF
@BOD_ON
@LVP_OFF
@CPD_OFF
@PROTECT_OFF

led var GPIO.0

i var byte 

Main:
For i = 0 to 255                                                 
Pwm GPIO.0,i,1
next i
if i = 255 then goto down

down:
for i = 255 to 1 step -1
pwm GPIO.0,i,1
next i
If i = 0 then goto main

Is the software command PWM supported on all chips ? I thought it simply pulses the pin for a duration and cycle.

Hope to hear from you guys soon

Cheers

Malcolm

[HenrikOlsson]

Hi Malcolm,
The 12F675 has comparators, which you correctly turned off with CMCON and VRCON but it also has an A/D and the the pin needs to be set to digital (I think).

Try setting the ANSEL register and set the port to output with the TRISIO register.

TRISIO.0 = 0   'Set GPIO.0 to output.
ANSEL.0 = 0    'Set GPIO.0 to digital.

I think that is your problem.

/Henrik Olsson.

[malc-c]

Thanks for the reply.

I've added those two lines to the code and I still get nothing out from the PIC.

The top section of the code is:

TRISIO.0 = 0   'Set GPIO.0 to output.
ANSEL.0 = 0    'Set GPIO.0 to digital		
GPIO.0 = 0
CMCON = 7 ' PortA Digital inputs
VRCON = 0        ' Voltage reference disabled
OPTION_REG.7 = 0

I've double checked the hardware and the PIC is receiving 5v, but all pins other than GP5 remain low (0.1v, with GP5 +2.6v) - could it be something to do with the internal OSC setting ?? - I want to use the built in 4 Mhz OSC

Malcolm

[sayzer]

Try these settings instead of yours especially for "RC_OSC_NOCLKOUT" ;

@ DEVICE PIC12F675, INTRC_OSC, WDT_OFF, MCLR_OFF,PROTECT_ON

[malc-c]

Try these settings instead of yours especially for "RC_OSC_NOCLKOUT" ;

@ DEVICE PIC12F675, INTRC_OSC, WDT_OFF, MCLR_OFF,PROTECT_ON

Thanks for the suggestion, but I now get a warning when I try to compile (using MPSAM) - it states "Found lable [DEVICE]" and "Illegal Opcode [12F675]"

[sayzer]

Thanks for the suggestion, but I now get a warning when I try to compile (using MPSAM) - it states "Found lable [DEVICE]" and "Illegal Opcode [12F675]"

In your code, put a space between '@' and "DEVICE"


--------------

[paul borgmeier]

change this

if i = 255 then goto down

to this

if i = 0 then goto down

and all should be well .....

or better yet delete the line (it adds no value) and replace the last line of the program shown with this

goto main

(instead of the if-then, which adds no value)

Paul Borgmeier
Salt Lake City, Utah
USA

[Acetronics2]

Hi, Malc

Don't you think a simple triangle slow wave generator based upon a 555 or a twin AOP could perfectly do the job ???

Note a simple bulb lamp could also do all the job itsef ... with a rectangular wave input.

mmmmh, back to the original idea ... you'll have to seriously slow down the PWM change rate ...

May be intended for some stop light for road/rail crossing, I presume ???

Alain

PS : and why not use a lookup table, just to reproduce exactly the truth ( exponential rise and fall of enlightment ) ???
just a " particular shape " wave generator ...in fact.

[malc-c]

Hi, Malc

Don't you think a simple triangle slow wave generator based upon a 555 or a twin AOP could perfectly do the job ???

Note a simple bulb lamp could also do all the job itsef ... with a rectangular wave input.

Quite possibly, however that wouldn't improve my understanding of PBP

May be intended for some stop light for road/rail crossing, I presume ???

Errr.. actually you don't want to know... Oh well all right..

A friend wants to model the Tardis from the BBC series Dr Who... and it has a slow pulsing light on top..... me and my big mouth offered to help, and like I said it works fine on a 16F628a, but I just need to port it to a 12F675

Malc