Not able to re-enable I2C interrupts after using spi.

[Newuser]

Hi All,

I have I2C & SPI sharing same lines.

I am using to I2C bus to communicate with another pic, and spi bus to read/write ext eeprom.

To write/read from eeprom using SPI, i am disabling I2C interrupts and then i am able to read/ write to EEPROM. But i am not able to bring back my I2C to communicate to the other PIC.
Here, my processor acting as a I2C slave.

So, my question is
How to bring up my i2c after using SPI??

Thanks a lot in advance.

Regards
Dwarag.

[PCM programmer]

You didn't specify your PIC, so I did a test for the 18F452.
The code which configures the MSSP module for hardware i2c
or SPI is shown below. Notice that there are certain things
in common between the two modes. The setup_spi() statement
changes some of the settings when it sets up the SPI mode.

You could create a routine called setup_i2c(), and simply
duplicate the #use i2c() setup code shown below. Use
the output_float() function to set the pins to inputs. Also
use #byte statements to define the addresses of the SSPCON
and SSPSTAT registers. Then write a line of code for each
one to load it with the correct value for i2c mode.
When you duplicate the i2c code, you might want to put in
a line at the start of it, to disable the SSP module, the same
way CCS does it in the setup_spi() function. This will reset
the module.

Then call the setup_i2c() function when you want to switch
back to using the MSSP module in i2c mode.

This is the initialization code that is inserted at the start of main()
when you specify the following #use i2c() statement.

[Ttelmah]

As one more comment, after setting up the I2C, I'd clear the interrupt flag. Remember the hardware for both functions is 'common', so this interrupt will occur for SPI character transfers, as well as for I2C transfers. After the SPI transactions, the flag will probably be set, but the contents of the registers will make little 'sense' to an I2C interrupt handler, and might lead to this getting very confused. Hence change the mode to I2C, then clear the interrupt, before re-enabling this.

Best Wishes

[New user]

Hi,

Thanks for the reply.

I am using PIC18f4680, i have tried your suggestion in my code. But, i couldn't re-enable the i2c interrupt yet.

Is it because of different processor?
If you have some examples in C code, please send it to me.

Thanks for your kind help


Regards
Dwarag.

[Newuser]

Thanks for your kind help.

After using spi, i overwritten the SSPCON register with value 0x36.
I could receive messages from the other pic, but was not able reply.

This problem is because of the overflow bit is set in the sspcon register, so in the interrupt handler i clear this bit, it worked for me.

So, if somebody facing this problem can try this method, it may help you.

Regards
Dwarag.