Datasheet

Seite 6
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SERIAL DIGITAL INTERFACE
Addressing
Every slave connected to the I
2
C-bus responds to a certain address. After generating
the start condition the master sends the address byte containing a 7bit-address
followed by a data direction bit (R/W). A ‘0’ indicates a transmission from master to
slave (WRITE), a ’1’ indicates a data request (READ).
The addressed slave answers with an acknowledge, all other slaves connected with
the I
2
C-bus ignore this communication.
The general HYGROSENS ASIC slave address is 0x78 (7bit). As the address is
completed with the R/W-Bit as LSB the address Byte (whole 8 bit) for reading data is
0xA1 for reading or 0xA0 for writing data to the ASIC.
By EEPROM programming it is possible to allocate and activate an additional arbitrary
slave address to every single device. In this case the device recognizes communica-
tion on both addresses, on the general one and on the activated one.
Write operation
During transmission from master to slave (WRITE) after the address byte follows a
command byte and, depending on the transmitted command, optional 2 data bytes.
The internal micro-controller evaluates the received command and processes the
related routine. The available commands are described in chapter 4.5.
optional
start
condition
slave
address
R/W
0
A
command
byte
A
1
st
data byte
A
2
nd
data byte
A
stop
condition
send by: master slave master slave master slave master slave master
Fig. 3: Write operation I
2
C
Read operation
After a data request from master to slave by sending an address-byte including a set
data direction bit the slave answers by sending data from the activated interface
output registers. The master must generate the transmission clock on SCL, the
acknowledges after each data byte (except after the last one) and finally the stop
condition.
A data request is answered by the interface module itself and does consequently not
interrupt the current process of the internal micro-controller. The data in the activated
registers is sent continuously until a stop condition is detected, after transmitting all
available data the slave starts repeating the data.
During running measurement cycle data is incessantly updated with conditioning
results. To get other data from slave (e.g. EEPROM contents) usually a certain
command has to be sent before the data request to initiate the transfer of this data to
the interface output registers. This command does interrupt the current process of the
internal microprocessor and consequently also a running measurement cycle.
optional
start
condition
slave
address
R/W
1
A
1st
data byte
A
2nd
data byte
A
… nth
data byte
stop
condition
sent by: master slave slave master slave master slave Master
Fig. 4: Read operation I
2
C