I2C Problem

Hi all,

I am trying to drive an I2C device from a windows CE board, unfortunately without success. I am trying the following test program...

void I2CStart() { // Initialize the unit

// put slave address in ISAR g_wISAR = 0x20;

// enable desired interrupts in ICR. // Arbitration loss detect interrupt NOT enabled


// enable i2c and scl g_wICR |= (ICR_IUE | ICR_SCLE);

// write to motor driver g_byIDBR = (0xb0);

// disable stop and arbitration in icr g_wICR &= ~(ICR_STOP | ICR_ALDIE);

// enable start and transfer byte in icr g_wICR |= ICR_START; g_wICR |= ICR_TB;


PrintI2C(); }

PrintI2C() is a very simple function that lists all the I2C registers. All but ISR have the expected values; ISR value is 0. I Think that at this stage it should have had the Transmit Empty flag enabled (?).

Controller I2C supply voltage is 3.3 volts, board is 5V. I am using a PCA9306 to shift levels. I have soldered two 2k2 (from SCL and SDA to supply) both sides.

Any Ideas please?

Thanks Best Regards

Carmel Gafa

Reply to
Loading thread data ...

So what are you observing or not observing? What's happening that you don't like?

Actually, I don't know if you need the level shifter. As long as you use 3.3 volts for the pullups and make sure your 5 volt device does not actively drive high, you should have no trouble with mixing 3 and

5 volt devices on the bus. A small series resistor on the 5 volt devices will protect everyone in case of a programming error. BTW, it is very likely that your board devices are 3.3 volt anyway. The 5 volts in is likely being converted to 3.3 volts to power most of the board. Not much is actually 5 volts these days.

One other comment, I don't know what devices you have on the bus, so I have no idea what the various control registers do or what the various constants are.

Reply to


Thanks for reply.

I am trying to connect an Arcom Viper to an MD22 motor driver board by robot-electronics.,

formatting link

I have found several articles where it is suggested to include a shifter, i agree with you, both pins are al 0V unless pulled up.....

Problem is that contents of ISR is 0 all the time. I would like , if possible, some verification that the code is correct.....

Thank you, Best Regards


Reply to

Hi, I think that problem is software related.... I connected a scope to monitor the SCL/SDA activity; and it was flat, nothing is happening.

I will greatly appreciate any help


Reply to

If you see no activity is the line high or low? A high line could be nearly anything, but if it is alway low, you either have no pullup resistor or one of the chips is misprogrammed and driving low all the time.

It would likely be easiest to test this by separating the units to verify each one independently. See if your master can write and you see a correct sequence. Then connect your slave and see if the bus gets clobbered. If it is correct with just the master and connecting the slave clobbers it, then you likely have a hardware problem with the slave. Else, you need to look harder at the master.

If the problem is in the master, try simplifying the code to directly control the output and toggle it. Keep breaking the system down to simpler pieces until it is obvious what is wrong.

Reply to

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.