Data Sheet

HYGROCHIP 2/3
DIGITAL HUMIDITY SENSOR
PROTOCOL DESCRIPTION I2C
MR (Measurement Requests)
By a measurement request command, the sleep
mode is terminated and the humidity module exe-
cutes a measurement cycle. The measuring cycle
begins with the temperature measurement, fol-
lowed by humidity measurement, digital signal
processing (linearizing, temperature compensation)
and finally writes the processed measured values
into the output register.
DF (Data Fetch)
The data fetch command serves to finish reading
the output register. The DF command is sent by the
master to the humidity module (slave) and begins
with the 7 Bit slave address. The 8th bit is 1 (=
read). The Humidity module sends back an ac-
knowledgement (ACK =0) in case of correct ad-
dressing.
The number of bits, that the humidity module sends
back, is completed when the master sends a NACK
(ACK= 1) and launches stop condition. The first two
bytes of measurement data contain the two status
bits as MSB, followed by the humidity value with 14
bits.
The MR command consists of the address of the
humidity module, with which the R/W bit is trans-
ferred as 0 (= write). After the humidity module is
answered with ACK (= measurement started), the
master finalized the transfer with NACK (ACK= 1)
and launches stop condition.
If temperature data is needed, these can be read
after the humidity value. The most significant 8 bits
of the temperature value will be transferred as third
byte. Then the least significant 6 bits of the tem-
perature value can be read as the fourth byte. The
last two bits are not used and should be masked
away.
The master has the possibility to terminate the
reading after each read byte through a NACK.
Hence, it is possible to finish reading even after the
first byte and evaluate only the status/stale bit and
the master can terminate the transfer without com-
pleting the whole cycle. If only the upper 8 bits of
the temperature value are to be transferred (8 bit
resolution), the transfer can be aborted after the
third byte by a NACK.