I can't get the interrupts to work

Guest · Posted: Fri Mar 21, 2008 7:48 am

Hi, I've been trying to get a 16F876A PIC to read data from an encoder but can't seem to get any of the interrupts to work. the serial port interrupt was working fine until yesterday but strangely stopped working. Could anyone please explain why the interrupts aren't working? bare in mind that I'm a newbie so please explain everything in detail please.

thanks in advance.

Here's the code I developed

Guest · Posted: Fri Mar 21, 2008 8:17 am

Start with the int_rda. This is terrible...
If you receive any character, above 'H', or below 'A', the routine will hang for ever, locking the processor up.
Rethink this.

Now the interrupt on change. There is a huge amount of c&*p here. First of all, it is pointless clearing, and disabling this interrupt in the routine. You _cannot_ clear this interrupt, _till the port is read_. Second, the compiler automatically clears the interrupt for you, when the routine is exited. There is no point in disabling the interrupt in the routine (since the flag is already set, it can't get set again...)_. Similarly there is no point in re-enabling it at the end. Just leave it unchanged.
Then, setting the tris. Since you don't specify 'use fast_io', the tris value _will_ be overridden as soon as you read the port. Since you are reading the port in the main all the time, the tris value _will_ immediately be set to 0xFF. Either use fast_io, set the tris just once (and the pull-ups, you don't need to set these in the interrupt), or get rid of all the extraneous tris operations.

Best Wishes

Guest · Posted: Fri Mar 21, 2008 8:36 am

thanks for the fast reply. like I said, I'm very new at this so I make lots of mistakes.

starting with the INT_RB, if I understood you correctly, the clear interrupt, disable interrupt and the enable interrupt inside the routine are useless. so I only need to enable the interrupt once in the main() outside of the while(TRUE) is that correct?
now the TRIS command. I did look at the fast_io command but couldn't get it to work properly. but from what I understould from your post, I can simply delete the tris command from the interrupt too, is that it?

thanks again for all the help.

Matro · Guest

Hi,

You well understood. But a lot of things in your program can't be understood. Even what you are trying to do.
If you are a newbie my advice is :
- clear all
- make your program step by step and test it every step
- give logical names to functions, variables and so on
- add comments
- very often refer to datasheet to understand what is happening in the PIC

Maybe try to say to us what your program needs to do, it could be simpler.

Other tips :
"#device icd = true" isn't needed if you don't use ICD as debugger.
if you want to use fast_io all port "tris" registers shall be initialized.

Matro.

Guest · Posted: Fri Mar 21, 2008 9:11 am

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

Your #use rs232() is incomplete. You need to specify how many bits you want to use. Plus, add ERRORS in it so any overrun will be automatically cleared. Try:
#use rs232(baud=115200,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8,errors);

You might want to try 9600 baud at first, just in case the higher baud rate might cause problems.

Since you're new to this, I would suggest you start your code with one section of code and work with it until you get it working. Then, add another section, or fuctionality, and work with it until it's doing what you want. Start simple and add one thing at a time. I would leave out the tris and fast_io stuff for now. Just let the compiler take care of that stuff until you get a better handle on the quirks of how the compiler does things.

Never enable/disable any of the interrupts while you're inside of one. Make your interrupt routines short and sweet. You want to get in, do something quick and then get out. If you need to do something extensive, set a flag in the interrupt routine and then poll that flag in main() and have whatever function called from there.

Good luck!

Ronald

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Ttelmah · Guest

"Since you're new to this, I would suggest you start your code with one section of code and work with it until you get it working. Then, add another section, or fuctionality, and work with it until it's doing what you want. Start simple and add one thing at a time. I would leave out the tris and fast_io stuff for now. Just let the compiler take care of that stuff until you get a better handle on the quirks of how the compiler does things. "

This is the best bit of general advice, both when learning, and when trying to debug things latter. Old comments about 'walk before trying to run', definately apply. Smile

Best Wishes

Matro · Guest

Try it instead of your ISR :

Guest · Posted: Fri Mar 21, 2008 10:55 am

thanks everybody for the replies. I'm quite surprised by the number of people that respond in this forum and the speed of the replies Very Happy

. I didn't expect so many programers of this kind of hardware.

I can now ount the number of impulses of the encoder and read time too, but only if I keep the set_tris_B (0x0f); comand in the INT_RB. if I delete that code line, I can only read the first impulse and the counter never goes beyond 1. should that happen?

from what I read in the datasheet, the PIC is a 8 bit processor so I shouldn't be able to count beyond 255, but one rotation of the encoder is over 1500 impulses. what I've been doing is when the counter passes 200 it restartes at zero and adds 1 to a second counter. since it's convenient for me to work with numbers higher than 255, is there another way to overcome this limitation?

Ttelmah · Guest

int16.....
Though the processor works natively in 8bit values (which is why the default 'int' is 8bit), the compiler is qute capable of working with 16bit values, if you declare them as such.
On the having to keep the tris in the int, switch to fast_io. What is happening is that every time you read the port, the tris is being changed. For something like an encoder, it is better to use fast_io, and set the tris up once.

Best Wishes

Matro · Guest

As said by Ttlemah, just use "int16" variables.
If you use fast_io, don't forget to initialize "tris" of ALL ports.
Finally if you really enjoy programming, be aware that built in functions and default options are maybe good for quick and simple programming but that you will obtain better code by programming everything yourself at a lower level (use directly registers, rewrite built in functions to match exactly your needs...).

Matro.

Ttelmah · Guest

No, you can set 'fast_io', on just one port. You don't have to change the others.
Generally, something like an optical encoder, is the only circumstance where it is worth usng this ability. Most of the time, the 'standard' handling is fine.

Best Wishes

Matro · Guest

You're right.
The correct sentence is "Don't forget to initialize tris of ALL ports concerned by the fast_io." ;-)
When I spoke about doing everything manually, I just think like a guy that program real-time, checking the ASM generated code and trying to optimize anything.
But maybe for most people the default generated code is sufficient. ;-)

Guest · Posted: Fri Mar 21, 2008 1:15 pm

Ttelmah and Matro, I've been trying the fast_io(b) but it doesn't seem to count. I wrote the #use fast_io(b) command
and in the main I put:
set_tris_b (0x0f);
but the counter only counts the first impulse from the encoder. any sugestions on how to correct this?
besides that problem, everything is working fine Smile

.
I'm going to start to look at the motors to see if I can figure out a way to get the current voltage and create a proportional derivative controller to adjust the voltage so to get the motor to spin at the desired velocity. If I have any problem I'll let you know ;)