General • Re: Unable to Read and Write in I2C

It sounds like, you have a misunderstanding about I2C:
What you try to do (based on your code):
a) master sends something and stops (e.g. with I2C SCL just for the CMD)
b) you expect that "master" gets something received (from a "slave" now starting to send)

I2C is always a "Master" and "Slave" relation:

• master provides SCL and sends a command
• master keeps providing SCL, can change direction for a READ, so that slave uses the same SCL (provided) by master, to send the response as a slave
• a slave never acts like a master, e.g. starting now to provide SCL (than it would be a master and the original master has to change into a slave mode)

There is not a "ping-pong" like one sends (as master) and now the other one (which was a slave) starts sending like a master.
Maybe you could, but you have to toggle the "master" (on both ends) to a "slave".

Usually, what happens is this:

• A master sends a CMD, e.g. writing a register address where it wants to read from
• it keeps clocking, with a RESTART, so that the slave can respond with sending now the register value

But a slave will never start itself by its own an I2C transaction. Than it would be a master (and the receiving device has to be a slave).

You need a "master - slave" relation, a "protocol", sending as master still all the time SCL, just changing direction between a WRITE and READ phase. And often, a READ from a slave happens after a RESTART signal (not as a separate, new I2C transaction).

Statistics: Posted by tjaekel — Sun Sep 01, 2024 9:24 pm

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