Starting I2c between Uno and Mega

Other Hardware 3rd Party Boards
1

I have a successful connection with Wire.h,
Uno as master and Mega as slave.
They both have a common structure, sending and receiving with

CommsStruct txData = {x, y};
Wire.beginTransmission(SLAVE_ADDR);
Wire.write((byte *)&txData, sizeof(txData));
Wire.endTransmission(true);

and

Wire.onReceive(receiveEvent);
Wire.readBytes((byte *)&rxData, sizeof(rxData));

I've noticed some issues when I power my cards a certain order, it doesn't work. Can I use something like

    Wire.begin(0);
    while (! Serial); 
    Wire.onReceive(receiveEvent);

In order to wait for a connexion before sending anything ?
while (! Serial); it waits for Serial, is there another method for I2C?

2

Please, give the example of the data item that you want to send from I2C-Master to I2C-Slave along with the postings of the sketches of both Master and Slave.

3

The thing is that you must always power up all boards at the same time. Then if you still get the problem include a two second delay at the start the setup function.

1 Like
4

You can keep roll calling the Slave until Master gets the ACK.

byte busStatus;
do
{
   Wire.beginTransmission(slaveAddr);   //avoid to use reserved address: 0x00 - 0x07
   busStatus = Wire.endTransmission();
}
while(busStatus != 0);
5

should the slave wait for the master or the master wait for the slave?

BTW: why do you need an UNO as add on to the MEGA. Why not simply put anything on the MEGA?

6

Or indeed put everything on the MEGA.

7

If OP would post his sketches, the readers could reproduce the faults and then to devise a possible solution.

8

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