AN2038

I2C emulation

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If a TIMEOUT occurs or a Stop condition is detected the state is forced to WAIT_START.

Each time a rising edge occurs on SDA occurs together with SCL in high state, a Stop

Condition occurs. In this case a flag is set indicating that new data has been received or

transmitted. This flag is used by the ProtoSup module.

When an SPI interrupt occurs a byte is received or transmitted.

If it is the first byte after the Start Condition, this byte will be analyzed to see if:

●

The Slave is addressed, this is the case if the address of the slave is equal to the

microcontroller I2C address.

●

If the transmission is a write from the master or a read from the slave. If it is the former,

the following bytes have to be read else the transmission buffer has to be transmitted

using SPI. The corresponding status flag is therefore set.

If the byte received is not the first byte, it is stored in a read buffer.

If an end of transmission interrupt occurs, the microcontroller has to validate the

transmission by detecting the master acknowledge.

The detection of master acknowledges will be performed in the SCL interrupt service routine

on falling edge.

After the detection of the master acknowledge a new byte in the transmission buffer will be

sent. If the buffer is empty, the condition is indicated setting a flag.