i2c Question

Joan · Joined: 29 May 2004 Posts: 41 Location: Barcelona, Spain

Hi guys:

some days ago I asked a question but nobody post any answer. Ok, I will do the question in another way, without any code example of my program.

I need to communicate 2 PIC's ( a pair of 16F88 with internal oscillator at 8 MHz ) with i2c protocol. The Slave mut be implemented by interrupt because its work is to generate 2 PWM's by software at high freq. Those days I've been search through the forum and I've been studying the codes and the protocol itself too.

I've implemented some codes but I haven't got luck. The only way to make the slave work it to use the i2c built in functions by software and put and aditional pin to do an interrupt ( IOC, Interrupt On Change ) on of the pins RB4 to RB7 and wait for incomming data. Something like the SPI Chip Slect pin ....

Anybody has implemented a project with this pic in slave mode that works ? ( I don't need any code, only the certain that is possible to do that ).

All the proves I'd done determines that i2c in slave mode with interrupt doesn't works or I've missing something important.

Please, can all the "experts" put their ideas or solutions ( I'm including the CCS Programmers) ? ( There is a lot of people with trhe same problem ).

Thanx in advanz.

Joan.

Neutone · Joined: 08 Sep 2003 Posts: 839 Location: Houston

IMHO the only way to get this working is to not use interupts or hand write them. Software PWM is not a resource hog at all. You can easily do software PWM while monitoring the I2C registers. For example;

davidpk · Joined: 29 Apr 2004 Posts: 13 Location: Opelika, AL

Joan,

I haven't ever used the I2C slave mode but the CCS manual says you must use the hardware for slave mode. (See the #use i2c in the pre-processor section)

Does this help?

David

falleaf · Joined: 23 May 2004 Posts: 48

A friend shared his examples to me, and I'm using it. I see it no problem, but I'm trying to understand how the C work.

That is, it seems to many I2C ASM examples, but so clear. See in thread "Need I2C examples"

I also posted a simple example there.

Joan · Joined: 29 May 2004 Posts: 41 Location: Barcelona, Spain

Hi guys:

Neutone
----------

Efectively I'm using a free delay running for the PWM's ( a "for" routine for each one, not timer0 interrupt that perhaps is a more elegant solution ) , they works well ( 600 Hz ) with a resolution of 1% ... it's enougth to drive 2 toys motors. But PWM are not the problem. I'd calculated the delay for reading the i2c incoming data and I only loose 2 cicles of PWM in all the process of interrupt routine. And I can see it with an oscilloscope.

David
--------

Yes, I used the statement

#use I2C(SLAVE, SDA=PIN_B1, SCL=PIN_B4, address=0xa0, SLOW, FORCE_HW)

But as I said in my previous message it's impossible to run it in this way.

falleaf
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I've seen lots of examples on the forum, revised the i2c protocol for the PDF file from PHILIPS and used all resources in the 16F88 that I can use for this pourpose, but I only can do it work in the way I said ( with IOC interrupt with an aditional pin and software i2c ).

I use the 16F88 not the 16F877 that you used. The main problem it that the PIC don't entry in the #int_SSP routine.

So, Neutone, David & falleaf, thanks for your posts.

The question: It is possible to run a 16F88 with internal oscillator at 8 MHz and Hardware i2c resources in slave mode ?

Regards.

Joan

falleaf · Joined: 23 May 2004 Posts: 48

I don't know muchie about C for PIC and don't know muchie bout 16F88. My old version of CCS C didn't support for 16F88 so I don't know.

However, if you only need to use, you can come to Nigel's tutorial and get the ASM code. It's very easy to use, just copy and paste. It's included the tutorial for software Slave mode.

In slave mode, you should use RB0 and any other pin as I2C port.

I used his code and used with 16F84A Smile

) no need SSP hardware.

If you need to understand, I'm newbie in C for pIC Smile