PNI RM3100 Sensor Suite - Manual (Page 27)

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RM3100 & RM2100 Sensor Suite User Manual Page 26 of 45
All communication is on the SDA line. The transaction is initiated by the host, or master,
sending the Start condition followed by the MagI2C’s slave address, and then the RW bit
is set to ‘0’, indicating a Write operation. The slave address is acknowledged by the
MagI2C by setting SDA to LOW. This is followed by the desired 7-bit register address
and then the register data. The register value automatically increments after every
received data byte. The transaction is terminated by the host sending the Stop condition.
The MagI2C will always acknowledge the start of an I
2
C Write transaction by sending a
‘0’ (i.e. the ACK signal). But if the Write command cannot be executed for some reason
the MagI2C will send a ‘1’ instead (i.e. the NACK signal). The reasons a NACK signal
might be sent are established by the HSHAKE register, and include writing to an
undefined register or writing to the POLL register while CMM is in progress, or vice
versa. See Section 5.6.2 for more information.
4.5.2 I
2
C Register Read
To perform a Read transaction, it is first necessary for the master to Write the desired
register address, and then to Read the register data. A generic transaction is given below.
START SLAVE ADDRESS RW ACK REGISTER ADDRESS (N) ACK STOP
S A6 A5 A4 A3 A2 A1 A0 0 0 A7 A6 A5 A4 A3 A2 A1 A0 0 P
From Host to MagI2C
From MagI2C to Host
START SLAVE ADDRESS RW ACK DATA FROM REG. (N) ACK DATA FROM REG. (N+1) NACK STOP
S A6 A5 A4 A3 A2 A1 A0 1 0 A7 A6 A5 A4 A3 A2 A1 A0 0 A7 A6 A5 A4 A3 A2 A1 A0 1 P
-------------- Data Transferred (n bytes + acknowledge) --------------
The Write sequence is described in the prior section, except for this case there is no data
to send. For the Read sequence the host again sends the MagI2C’s slave address, but this
time sets the RW bit is set to ‘1’. The MagI2C acknowledges that it is has been
addressed and then sends data from the register address that was previously sent. The
host acknowledges receipt of the data, and then the MagI2C increments the register
address and sends data from this register. This continues until the host sends the NACK
command followed by the Stop command, which terminates the transaction.