FDA903D datasheet(60/82 Pages) STMICROELECTRONICS

60 / 82 page

I2C bus interface

FDA903D

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DocID031502 Rev 2

14.1

Writing procedure

There are two possible procedures:

without increment: the I bit is set to 0 and the register is addressed by the subaddress.

Only this register is written by the data following the subaddress byte.

with increment: the I bit is set to 1 and the first register write is the one addressed by

subaddress. The registers are written from this address up to stop bit or the reaching of

last register.

14.2

Reading procedure

The reading procedure is made up only by the device address (sent by master) and the data

(sent by slave) as reported in Figure 71 (a). In particular when a reading procedure is

performed the first register read is the last addressed in a previous access to I2C peripheral.

Hence, to read a particular register also a sort of write action (a write interrupted after the

sub-address is sent) is needed to specify which register has to be read. Figure 71 (b) shows

the complete procedure to read a specific register where:



the master performs a write action by sending just the device address and the

subaddress; the transmission must be interrupted with the stop condition when the

subaddress is sent.



now, the read procedure can be performed: the master starts a new communication

and sends the device address; then the slave (FDA903D) will respond by sending the

data bits.



the read communication is ended by the master which sends a stop condition preceded

by a not-acknowledge.

Instead, performing a start immediately after the stop condition could be possible for

generating the repeated start condition (Sr) which also keeps busy the I2C bus until the stop

is reached (Figure 71 (c)).

Figure 71. Reading procedure

There are two possible reading procedures:

without auto-increment (Figure 72 (a)) if the "I" bit of the last I2C writing procedure has

been set to 0: in this case only the register addressed by the sub-address sent in the

previous writing procedure is read;

with auto-increment (Figure 72 (b)) if the "I" bit of the last I2C write procedure has been

set to 1: in this case the first register read is the one addressed by sub-address sent in

the previous writing procedure. Only the registers from this address up to the stop bit

are read.

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