MS8607-02BA01 PHT Combination Sensor
DA8607-02BA01_003 www.meas-spec.com July 7th, 2015
000086072885 ECN2515 15/21
MEASURE RH HOLD/NO HOLD SEQUENCE
MS8607 has t wo different operation modes to measure relative humidity (RH): Hold Master m ode and No Hold
Master mode.
No Hold Master mode allows for processing other I²C comm unication tasks on a bus while the humidit y sensor
is m eas uring. Fi gure 18 and 19 illustrat e t he c om munication s equ ence of both modes. I n th e H o ld Mas ter mode,
the humidit y sensor pulls down the SCK lin e while measuring to for ce the master into a wait s tate. By releasing
the SCK line, the humidity sens or indicates t hat internal processing is com pleted and that tr ansm ission may be
continued.
In the No Hold Master mode, the MCU has to poll for the termination of the internal processing of the humidity
sensor. This is done by sending a start condition followed by the I²C header (0x81) as shown below. If the
internal pr ocessing is f inished, the humidity sensor ack nowledges the pol l of the MCU and d ata can be read by
the MCU. If the meas urement pr ocessing is no t finished, t he humidit y sensor answers the Not Acknowledge bit
and start condition must be issued once more.
For both modes, the measurement is stored into 14 bits. The two remaining least significant bits (LSBs) are
used for transmitting status information. Bit1 of the two LSBs must be set to ‘1’. Bit0 is currently not assigned.
100000000111001010
S W A A
100000010 XXXXXXXX0XXXXXX100
S R A A A
100101110 From M aster S = St art Condi t i on W = Write A = Ack nowl edge
From S l ave P = St op Conditi on R = Read N = Not A ck nowl edge
Chec ksum N P On hol d
Figure 18: I2C M easur e RH Hold Master communication sequence
100000000111101010
S W A A
100000010XXXXXXXX0XXXXXX100100101110
S R A A A Checks um N P
From M aster S = Start Condi t i on W = Write A = Ack nowl edge
From S l ave P = Stop Condit i on R = Re ad N = Not Ack nowledge
Figure 19: I2C Measure RH No Hold Master communication sequence
For Hold Mas ter seq uenc e , t he Acknowledge bit that follo ws the Sta tus bi t may be chang ed t o Not Ac k nowledge
bit followed by a stop condition to omit checksum transmission.
For No Hold Master sequence, if measurement is not completed upon “read” command, sensor does not
provide ACK on bit 27 (more of these iterations are possible). If bit 45 is changed to NACK followed by stop
condition, checksum transmission is omitted.