I2C and CAN protocols not working

Hi Andrew Neil,

Thanks for your reply. I have tried with I2C LCD and that is also not communicating and I have tested the same code with another controllers and there its working. I have doubt that any pull-up resistors do I need to connect externally, because SDA and SCL pins are directly taken from LPC1768 IC to the external pins without any other component connected. Anyway I will follow your suggestions given in the above thread and try to do some additional work.

Hi Andrew Neil,

Thanks for your reply. I have tried with I2C LCD and that is also not communicating and I have tested the same code with another controllers and there its working. I have doubt that any pull-up resistors do I need to connect externally, because SDA and SCL pins are directly taken from LPC1768 IC to the external pins without any other component connected. Anyway I will follow your suggestions given in the above thread and try to do some additional work.

Hi Andrew Neil,

I have tested I2C based LCD and its working without any external pull-up resistors. And the I2C based LCD is working fine with the each micro-controller. Now I will try to check with both micro controllers connected with I2C. Anyway thanks for your support.

So that tells you that there must be internal pullups somewhere, then - doesn't it?

"the I2C based LCD is working fine with the each micro-controller"

So, in both of those cases, the microcontroller is being the Master - isn't it?

"I will try to check with both micro controllers connected with I2C"

For that, one of the microcontrollers will need to be a Slave - won't it?

And don't forget the pullups ...

Hi Andrew Neil,

So that tells you that there must be internal pullups somewhere, then - doesn't it?

""That is true. But I am thinking that pull-up resistors may be added in I2C LCD driver. And from my basic knowledge any one device must have pull-up resistors inorder to I2C bus to function. Because again if I tried with both microcontrollers, I2C between microcontrollers is not working.""

"the I2C based LCD is working fine with the each micro-controller"
So, in both of those cases, the microcontroller is being the Master - isn't it?

""Yes. You are absolutely true. And only master program has been flashed to the microcontroller and LCD is like almost passive device to respond to the master transactions.""

"I will try to check with both micro controllers connected with I2C"
For that, one of the microcontrollers will need to be a Slave - won't it?

""I have flashed one microcontroller with master-transmitter program and another microcontroller with slave-receiver program. But still I2C is not working between microcontrollers"".

And don't forget the pullups ...

""Please elaborate this last suggestion and I am not getting what exactly it is. And if want to add external pull-up resistors then what are the resistor values have to choose.""

Hi Andrew Neil,

I have connected external pull-up resistors (i.e. 4.7K-Ohm) in both SDA and SCL lines of I2C using board 3.3V supply. And now the I2C interface is working fine between two microcontrollers also. It seems to be I2C LCD driver might have included inbuilt pull-up resistors and that's the reason I2C LCD worked fine without any problem. Anyway thanks for your guidance and support.

Yes, that would seem the obvious conclusion from what you posted on 6-Nov-2018 18:04 GMT.

Hi Andrew Neil,

I am trying to use external interrupt with the following code using LPC1768 micro controller. I have connected P2.10 and P2.11 to switches and GPIO0 used to connect the LED's. When I press the switches no LED is going on Port 0. But after pressing reset the LEDs are glowing twice because of only reset button. And the code is shown below for your suggestion. I have posted in another thread but no one is helping and requesting to see this problem.

   #include<LPC17xx.h>

        #define EXTMODE0        0
        #define EXTMODE1        1

        #define EXTPOLAR0       0
        #define EXTPOLAR1       1

        #define EINT0_PIN       20
        #define EINT1_PIN       22

        void delay(unsigned int value)
        {
                unsigned int i, j;
                for(i = 0; i < value; i++)
                for(j = 0; j < 2500; j++);
        }

        void EINT0_IRQHandler()
        {
                LPC_SC->EXTINT = (1<<0);  //clearing interrupt bit
                LPC_GPIO0->FIOSET = 0xffffffff;
                delay(1000);
                LPC_GPIO0->FIOCLR = 0xffffffff;
                delay(1000);
        }

        void EINT1_IRQHandler()
        {
                LPC_SC->EXTINT = (1<<1); //clearing interrupt bit
                LPC_GPIO0->FIOSET = 0xffffffff;
                delay(1000);
                LPC_GPIO0->FIOCLR = 0xffffffff;
                delay(1000);
        }

        int main()
        {
                LPC_SC->EXTMODE = (0<<EXTMODE0)|(0<<EXTMODE1);  //level-sensitive mode
                LPC_SC->EXTPOLAR = (0<<EXTPOLAR0)|(0<<EXTPOLAR1); //low active state
                LPC_PINCON->PINSEL4 = (1<<EINT0_PIN)|(1<<EINT1_PIN);  //switches connected to P2.10 and P2.11

                LPC_GPIO0->FIODIR = 0xffffffff;

                NVIC_EnableIRQ(EINT0_IRQn);
                NVIC_EnableIRQ(EINT1_IRQn);

                while(1);
        } </prep