Gee Whiz, Olin, I'll check with you first next time, OK?
What I said is the way my I2C works. Nobody was answering
so I took a crack at it.

--Bob
 
Olin Lathrop wrote:

>Bob Axtell wrote:
>  
>
>>The ACK signal is the way that the Master knows that everything is
>>working.
>>    
>>
>
>It is important to distinguish between master/slave and sender/receiver.
>The ACK bit is always driven by the receiver, whether that is the master or
>the slave.
>
>  
>
>>3. Usually there are one or more bytes of address bytes (depends on
>>what the
>>SLAVE chip does)
>>    
>>
>
>There are only 2 types of IIC addresses, 7 bit and 10 bit.  I've found chips
>that support only 7 bit to be far more common.  While it is possible that
>there is an additional address byte since 10 bit addressing could be used, I
>would NOT say that it is "usual".  For most ordinary purposes you can
>consider IIC to be a 7 bit addressed bus and forget about 10 bit address
>mode.  In no cases are there more than 2 address bytes.
>
>  
>
>>4. Finally, if data is to be written to the slave, it acknowledges
>>that
>>it is taking
>>each byte by pulling down during the 9th. When the chip can no longer
>>take anymore data, it no longer acknowledges by pulling down,
>>indicating to the Master that fact.
>>    
>>
>
>This is correct.  I just want to point out that this is only one way of
>ending a write sequence.  The master can chose to stop at any time by
>issuing a BUS STOP, whether the slave ACKed the last byte or not.
>
>  
>
>>2. In order to set the address before sending the data, the read
>>cycle looks exactly like a WRITE transmission, except that after the
>>addresses are sent, the Master issues a STOP FLAG.
>>    
>>
>
>No!  Whether a IIC sequence is a read or a write is indicated by the LSB of
>the first address byte.  Both master and slave then know which direction
>subsequent bytes will be sent.  When the master writes a BUS STOP, the IIC
>sequence is over.  Any new sequence will need to start with a new BUS START
>and address byte, and therefore can be read or write indpendently of the
>previous.  In IIC, there is no requirement to preserve state from before the
>last BUS START or BUS STOP.  Whatever happens in one sequence has no effect
>on the next as far as the IIC bus is concerned.
>
>  
>
>>This transmission scheme, developed in the 1970s to send control info
>>on TV chassis, remains to this day the most efficient 2-wire
>>signalling method ever
>>developed.
>>    
>>
>
>That's a very general statement, which is neither useful nor correct.  IIC
>can be a good solution to particular problems, but can't possibly be the
>"most efficient" because each application has its own set of tradeoffs and
>"efficiency" will have many different meanings in different contexts.
>Comparing IIC to RS-485 to CAN, for example, outside the context of a
>particular problem is like comparing apples to cars to fenceposts.
>
>
>*****************************************************************
>Embed Inc, embedded system specialists in Littleton Massachusetts
>(978) 742-9014, http://www.embedinc.com
>  
>


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