RBI Series
Pressure sensors with analog and digital output
5/9
E / 11718 / A
www.sensortechnics.com
INTRODUCTION
The RBI is capable to generate a digital output signal. It
runs a cyclic program, which will store a corrected 12-bit
sensor value about every 10 ms within the output registers
of the internal ASIC. In order to use the pressure transducer
for digital signal readout, the device should be connected
to a bidirectional I²C-bus.
According to the I²C-bus communication specification, the
bus is controlled by a master device, which generates the
clock signal, controls the bus access and generates START
and STOP conditions. The RBI is designed to work as a
slave, hence it will only respond to requests from a master
device.
The I²C-bus master-slave concept requires a unique
address for each device. The RBI has a hard coded slave
address (1111000xb), therefore it is not possible to access
more than one RBI on the same I²C-bus line.
DIGITAL I2C INTERFACE
The RBI complies with the following protocol (FIGURE I):
Bus not busy: During idle periods both data line (SDA) and
clock line (SCL) remain HIGH.
START condition (S): HIGH to LOW transition of SDA line
while clock (SCL) is HIGH is interpreted as START con-
dition. START conditions are always generated by the
master. Each request for the current pressure value must
be initiated with a START.
STOP condition (P): LOW to HIGH transition of SDA line while
clock (SCL) is HIGH determines STOP condition. STOP
conditions are always generated by the master. More than
one request for the current pressure value can be trans-
mitted without generation of intermediate STOP condition.
DATA valid (D): State of data line represents valid data when,
after START condition, data line is stable for duration of
HIGH period of clock signal. Data on line must be
changed during LOW period of clock signal. There is
one clock pulse per bit of data.
Acknowledge (A): Data is transferred in pieces of 8 bits
(1 byte) on serial bus, MSB first. After each byte receiving
device – whether master or slave – is obliged to pull
data line LOW as acknowledge for reception of data.
Master must generate an extra clock pulse for this pur-
pose. When acknowledge is missed, slave transmitter
becomes inactive. It is on master either to send last com-
mand again or to generate STOP condition in that case.
Slave address: Each device connected to the bus has a
unique slave address. After generating a START con-
dition, the master has to transmit the slave address for
the RBI with a READ command: $F1. The RBI must not
be accessed with a WRITE command ($F0) as the
correct function of the device can not be guaranteed in
this case (note: a power-down power-up change will
force the sensor to use factory data again).
DATA operation: The RBI starts to send 2 data bytes containing
the current pressure value placed in the output registers.
FIGURE I: I²C-BUS Protocol
SDA
SCL
START
condition
Data
valid
Data allowed
to change
STOP
condition
R/W
S
Data Byte 1
A
Data Byte 2
Slave Address
A
1
S
P
Slave Address
generated by master
generated by slave
S = START condition
A = Acknowledge
P = STOP condition
Data Byte 1 = High Byte (MSB first)
Data Byte 2 = Low Byte (LSB last)
Read out of pressure value
Next command
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