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PIC18F27J53 LED Blinky code

 
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djsb



Joined: 29 Jan 2011
Posts: 34

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PIC18F27J53 LED Blinky code
PostPosted: Fri Apr 28, 2023 10:40 am     Reply with quote

Hi,
I'm trying to get my CCS PCH (V5.115) compiler set up with MPLABX V6.05 (which also has PCM V5.110 installed). I'm using a PIC18F27J53 to start with on a simple PCB breakout. Does anyone have a basic LED Blinky example I can try (or point me to an example, maybe provided with the compiler). Just want to get the basic fuses setup and the external ceramic resonator. I've seen a few more advanced code on the forum that use pin select functionality. I don't need to use that yet, but an example using a switch input would be a bonus. Any help appreciated. Thanks.

David.
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Fri Apr 28, 2023 11:03 am     Reply with quote

Just try.
Any of the flash an LED examples given here ought to work, However
one critical thing is needed, that you have not said. The frequency of your
resonator.
Ceramic resonators are setup exactly the same as crystals.

So start with something like:
[url]
https://www.ccsinfo.com/forum/viewtopic.php?t=59170&highlight=flash+led
[/url]

Change the clock setup to use
CRYSTAL=FREQUENCY_OF_YOUR_RESONATOR

Once this is working, and working at the right frequency, program a
pin for your 'switch'. Have this wired to pull an input low. Add a pullup
on this. Now portB on your chip does support internal programmable
pull-ups. On the whole port though a search on pullup in the manual
will find this. They try changing the delays in the loop to use a variable,
and at the start of each loop, read the input on the pin which you use
for the switch, read this and if it is 1, set one value, and if 0 a
different value. This way you can then see the flash rate change when
your switch is operated.
djsb



Joined: 29 Jan 2011
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PostPosted: Fri Apr 28, 2023 11:43 am     Reply with quote

Thanks Ttelmah,
I'll start first with reading the header file to see which fuses to set. I like to proceed with caution in case I lock myself out with code protection. The resonator is 16MHz by the way.
Ttelmah



Joined: 11 Mar 2010
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PostPosted: Sat Apr 29, 2023 1:31 am     Reply with quote

Don't get too neurotic about the protection. A full erase will clear the
protection. Very Happy
djsb



Joined: 29 Jan 2011
Posts: 34

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PostPosted: Sun May 07, 2023 7:22 am     Reply with quote

I've just tried this code, which I admit is just a copy and paste from an example in this forum.

Code:

#include <18F27J53.h>
#device ADC=12                                   
#fuses  HSPLL,PLLEN,PLL5, NOCPUDIV, NOWDT,NOPROTECT                     
#fuses  ADC12, RTCOSC_INT, DSWDTOSC_T1                           
#use    delay(clock=8000000)

#use    rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

void main() {
   
    while(TRUE)
      {
       output_high(PIN_B6);
       delay_ms(1000);
       output_low(PIN_B6);
       delay_ms(1000);
      }
           
}


This gives me a square wave with a period of 832ms (on/off for 416ms). The dev board I'm using has an 8MHz crystal (I changed the board). I'd like to learn how to use both the internal RC oscillator AND the external clock. I'm obviously going to have to read the manual to figure out which fuses to set/clear. Can anyone give me some pointers in the right direction. Thanks.

David.
temtronic



Joined: 01 Jul 2010
Posts: 9081
Location: Greensville,Ontario

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PostPosted: Sun May 07, 2023 8:51 am     Reply with quote

In the datasheet, locate the block diagram for the 'clock'. You'll see all the different paths a 'clock' can follow......
I printed that page of for the 18f46k22 years ago as they're quite complicated compared to the 16C84 PICs...... Smile
Ttelmah



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PostPosted: Sun May 07, 2023 10:29 am     Reply with quote

First thing, on most of the chips you can only use one clock _OR_ the
other. Not AND.
What would be the point anyway?. If you have the better accuracy of
a crystal fitted, using the intenal oscillator would be pointless.

That said, the easiest way to setup for each is:
Code:

#fuses  HSPLL,PLLEN,PLL5, NOCPUDIV, NOWDT,NOPROTECT                     
#fuses  ADC12, RTCOSC_INT, DSWDTOSC_T1                           
#use    delay(clock=8000000)
//This is wrong. The PLL on this chip is designed to give 96Mhz for the
//USB. The settings are wrong for your clock, and the CPU will not
//be running at 8MHz if it did work.
//For 8MHz crystal, you need to use PLL2 Table 3-5 in the datasheet.
//For an 8MHz CPU frequency you then need CPUDIV6
//The PLL is only designed to accept 4MHz (so 8MHz/2). Then the
//CPU is divided from this /2. So CPUDIV6 gives 96/(2*6) = 8MHz

#fuses  HSPLL,PLLEN,PLL2, CPUDIV6, NOWDT,NOPROTECT                     
#fuses  ADC12, RTCOSC_INT, DSWDTOSC_T1                           
#use    delay(clock=8000000)

//Much easier and safer to use:
#fuses  NOWDT,NOPROTECT                     
#fuses  ADC12, RTCOSC_INT, DSWDTOSC_T1
#use    delay(CRYSTAL=8MHz, CLOCK=8MHz, USB_FULL)
//This will automatically set the fuses up for this

//or
#fuses  NOWDT,NOPROTECT                     
#fuses  ADC12, RTCOSC_INT, DSWDTOSC_T1
#use    delay(INTERNAL=8MHz, CLOCK=8MHz, USB_FULL, ACT)
//This sets up the internal oscillator to run at 8MHz, and enables
//active clock tuning (needed for USB with the internal oscillator)

//then you have choices of faster clock rates from the same crystal
//8, 16, 24 or 48MHz are supported from this crystal
#fuses  NOWDT,NOPROTECT                     
#fuses  ADC12, RTCOSC_INT, DSWDTOSC_T1
#use    delay(CRYSTAL=8MHz, CLOCK=16MHz, USB_FULL)


You need to really study the datasheet, and look at what options
are actually supported for a particular crystal. Only use the legal
settings if you want it to work.

This PLL will run a small margin away from it's rated frequency, but
not a lot. USB will only work if it is running at 96MHz.


Last edited by Ttelmah on Sun May 07, 2023 10:44 am; edited 2 times in total
djsb



Joined: 29 Jan 2011
Posts: 34

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PostPosted: Sun May 07, 2023 10:42 am     Reply with quote

Thank you, Ttelmah and temtronic,
I appreciate the clear explanation provided.
I will definitely read the datasheet as suggested, starting with the block diagram and then delving more deeply. Have a nice day.
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