Datasheet

Seite 3
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SERIAL DIGITAL INTERFACE
1 General Description
The HYGROSENS ASIC includes a serial digital interface, which is able to communi-
cate using two different communication protocols – I
2
C and SPI –communication. The
serial digital interface allows the programming of the EEPROM to configure the appli-
cation mode of the ASIC and to calibrate the conditioning equation. Furthermore it
makes possible the read out of the conditioning result of measurand and both temper-
atures as digital 15 Bit values. The ASIC works always as slave. The used communi-
cation protocol has to be chosen by programming EEPROM. There are also
commands to change the valid communication mode. Only one communication
protocol is valid at one time. The implemented commands are available in all commu-
nication modes but are divided in two sets with different validity. Commands, which
change the configuration of the device, are suppressed in “Normal Operation
Mode” (NOM) and are available only after changing to “Command Mode” (CM). A non-
configured device, identified by a CRC Error regarding EEPROM contents, starts up in
a special mode so that communication by any of the available protocols is possible.
After power-on a 20ms-time-slot is opened to start Service-communication. If no
Service-communication is detected, the serial digital interface changed in a mode in
which it can receive commands in I
2
C-mode as well as in SPI-mode. If it is necessary
to read out data from a non-configured device (transmission by slave), the used
communication protocol has to be explicitly defined by sending a certain command.
Note that the HYGROSENS ASIC also do not send acknowledges in non-configured
mode if I
2
C-communication is used. If the HYGROSENS ASIC receives a valid
command at the serial digital interface the measurement cycle is interrupted because
the internal micro-controller has to execute the requested command routine. An
exception is a read-request. The HYGROSENS ASIC answers without interrupting the
measurement cycle. This makes possible the read-out of the digital conditioning
results during measurement cycle. A command consists of an address byte and a
command byte. Additionally the commands for writing the EEPROM or its mirror in the
RAM enclose two data bytes. This is independent from used communication protocol.
To read data from the HYGROSENS ASIC (e.g. EEPROM contents) usually a certain
command has to be sent to transfer this data into the output register of the serial inter-
face. Thereafter the READ command consisting of the address byte with the read bit
set is used to get this data. The data are transmitted continuously repeated as long as
the master send the clock and do not abort by generating a stop condition. Again this
is independent from used communication protocol. During the measurement cycle the
HYGROSENS ASIC transfers the conditioning results into the output registers of the
serial digital interface. There are three registers for humidity and both temperatures.
The activation of these registers and consequently of the transmitted data have to be
set by EEPROM programming. The results are sent in the sequence humidity, temper-
ature 1 and temperature 2 according to the register activation if the master sends a
read-request.