Technical Note
Sleep Mode for Use with Honeywell Digital Pressure Sensors:
ASDX Series, APB Series, and Trustability® HSC, SSC Series
1.0PURPOSE
The purpose of this technical note is to provide the information
necessary for using Sleep Mode in the ASDX Series, ABP Series
and TruStability™ HSC Series and SSC Series Digital Output
Pressure Sensor products.
Full Measurement Request (FMR) and Pressure Measurement
Request (PMR) commands are given in Section 4.0.
2.0OVERVIEW
Sleep Mode is a special factory set mode of the pressure sensor
that allows the sensor to power down between necessary
pressure readings. By implementing this mode, current
consumption during the non-measurement time of the sensor
can be reduced from 2.5 mA typ. to 0.5 μA typ.
•
A FMR or PMR wakes the sensor and starts a measurement
cycle.
FMR: The sensor performs a full measurement and
calculation cycle, including all secondary measurements
(temperature and A/D auto-zero).
PMR: The sensor measures only the sensor bridge and
performs the correction calculations using previously
measured temperature and auto-zero data. Valid output
values are then written to the digital output register and the
sensor powers down again.
•
This is ideal for applications where current consumption is more
important than speed, such as battery-powered applications.
The sensor only “wakes up” when sent a special command over
the I2C or SPI digital communication buses, depending on the
type of digital output sensor.
Following a measurement sequence, and before the next
measurement can be performed, the master must send a Read
Data Fetch (RDF) command, which will fetch the data as 2, 3
or 4 bytes (see Section 4.0), without waking the sensor. When
an RDF is performed, the data packet returned will be the last
measurement made with the status bits set to “valid”. After
the RDF is completed, the status bits will be set to “stale”. The
next FMR or PMR will wake the sensor again and start a new
measurement cycle.
3.0
DESCRIPTION (see Figure 1)
In Sleep Mode, following the power up sequence, the
sensor will power down again until the master sends a “Full
Measurement Request” (either I2C or SPI) or a “Pressure
Measurement Request” (I2C only) command. Specifics on the
Figure 1. System Timing
Sensor core activity
POR Startup
Approx. 1.26 ms
Power Down
Full
Measurement
Request
Digital interface activity
Measure Measure Measure CalculaTemp. Auto-zero Bridge
tions
PowerDown
Down
Power
FMR wakes
sensor
FMR wakes
sensor
FMR
RDF
Full
Measurement
Request
RDF
Read
Data
Fetch
Read
Data
Fetch
Read here returns
invalid data
POR Startup
Power Down
Pressure
Measurement
Request
Digital interface activity
Measure CalculaBridge
tions
PMR
PowerDown
Down
Power
Measure
Temp.
PMR wakes
sensor
RDF
Read
Data
Fetch
RDF
Read
Data
Fetch
Read here returns
invalid data
Sensing and Control
Read here returns
valid data
PMR wakes
sensor
Pressure
Measurement
Request
FMR
Full
Measurement
Request
Approx. 460 us
Sensor core activity
Measure
Temp.
PMR
Pressure
Measurement
Request
Read here returns
valid data
Technical Note
Sleep Mode for Use with Honeywell Digital Pressure Sensors:
ASDX Series, APB Series, and Trustability® HSC, SSC Series
If an RDF is sent while the measurement cycle is still in progress,
then the status bits of the packet will read as “stale”. The sensor
should be polled at a frequency slower than 20% more than the
Sleep Mode response shown in Table 1.
Table 1. Sleep Mode Response Times1
Response Time
1.5 ms
Figure 3. Command Structure for I2C PMR
Start
Pressure Measurement Request (PMR)
0.5 ms
Note 1. Times are typical. For worst case, multiply by 1.15 (15%
frequency variation).
In I2C mode only, the INT pin of the sensor will assume an
interrupt function. This allows the user to monitor the interrupt
pin instead of continually polling the output looking for valid
data. The interrupt will indicate that the measurement and
calculations are complete, and that new valid data is ready to be
read on the I2C interface. (This function is only available for DIP
and SMT versions.)
4.0
4.1.I2C Measurement Request Commands
4.1.1. Full Measurement Request (FMR)
The command structure shown in Figure 2 is used to wake the
sensor from sleep mode and perform a full measurement cycle,
including secondary measurements.
Read
S TOP
Slave Address [6:0]
ACK
Start
Figure 2. Command Structure for I2C FMR
1
Bits generated by master
Bits generated by slave (sensor)
The command begins with a Start bit, followed by the seven
bit address, followed by a “1”, indicating a Read. The master
then waits for the sensor to generate an Acknowledge, and then
immediately generates a Stop condition.
2
sensing.honeywell.com
0
Slave Address [6:0]
Write
Bits generated by master
Bits generated by slave (sensor)
The command begins with a Start bit, followed by the seven
bit address, followed by a “0”, indicating a Write. The master
then waits for the sensor to generate an Acknowledge, and then
immediately generates a Stop condition.
SLEEP MODE COMMANDS
A6 A5 A4 A3 A2 A1 A0
A6 A5 A4 A3 A2 A1 A0
S TOP
Full Measurement Request (FMR)
ACK
Measurement Request
4.1.2. Pressure Measurement Request (PMR) Command
The command structure shown in Figure 3 is used to wake the
sensor from sleep mode and to perform a partial measurement
cycle without secondary measurements. This measurement is
faster than the FMR but potentially less accurate because it uses
previously stored values for temperature and A/D auto-zero.
4.2.
SPI Full Measurement Request (FMR) Command
Because the SPI protocol is only half duplex, there are no Write
conditions for the bus. Because of this, only the FMR command
is available in SPI mode. Also, because of the read-only nature
of SPI for Honeywell pressure sensors, the command is
executed in a different manner.
The SPI FMR only requires that the SS line be dropped low for
a minimum of 8 μs, then raised high again. The rise of SS will
trigger the sensor to power up and perform the measurements
(see Figure 4).
Figure 4. SPI FMR Command
SS
8 μs
Technical Note
Sleep Mode for Use with Honeywell Digital Pressure Sensors:
ASDX Series, APB Series, and Trustability® HSC, SSC Series
4.3.I2C Read Data Fetch
The I2C Read Data Fetch (RDF) command is exactly the same
command that is used in the normal update (continuous) sensor
mode to retrieve the data from the sensor. Data can be read
out from the sensor in either two, three or four byte amounts,
depending on whether temperature data is needed, and to what
resolution.
The command structure for these different reads is shown in
Figure 5. For more information regarding I2C read commands,
please consult:
“I2C Communications with Honeywell Digital Output Pressure
Sensors” Technical Note.
Figure 5. I2C Read Data Fetch Command Structures
Two Byte Data Readout
Status
Bridge Data [13:8]
S TOP
Read
Data Byte 2
B7 B6 B5 B4 B3 B2 B1 B0
NACK
Slave Address [6:0]
S1 S0 B13 B12 B11 B10 B9 B8
ACK
1
ACK
Start
Data Byte 1
A6 A5 A4 A3 A2 A1 A0
Bridge Data [7:0]
Three Byte Data Readout
Status
Bridge Data [13:8]
Bridge Data [7:0]
S TOP
Data Byte 3
T10 T9 T8 T7 T6 T5 T4 T3
NACK
Read
Data Byte 2
B7 B6 B4 B5 B3 B2 B1 B0
ACK
Slave Address [6:0]
S1 S0 B13 B12 B11 B10 B9 B8
ACK
1
ACK
Start
Data Byte 1
A6 A5 A4 A3 A2 A1 A0
Temperature Data [10:3]
Four Byte Data Readout
Bits generated by master
Status
Bridge Data [13:8]
Bridge Data [7:0]
Temperature Data [10:3]
NACK
Data Byte 4
T2 T1 T0 X X X X X
S TOP
Data Byte 3
T10 T9 T8 T7 T6 T5 T4 T3
ACK
Read
Data Byte 2
B7 B6 B5 B4 B3 B2 B1 B0
ACK
Slave Address [6:0]
S1 S0 B13 B12 B11 B10 B9 B8
ACK
1
ACK
Start
Data Byte 1
A6 A5 A4 A3 A2 A1 A0
Temperature Data [2:0]
Bits generated by slave (sensor)
4.4.
SPI Read Data Fetch
The SPI Read Data Fetch (RDF) is exactly the same as is used
in the normal update (continuous) sensor mode to retrieve the
data from the sensor. Data can be read out from the sensor in
either two, three, or four byte amounts, depending on whether
temperature data is needed, and to what resolution.
The command structure for these different reads in Figure 6. For
more information regarding SPI data, please consult:
“SPI Communication with Honeywell Digital Output Pressure
Sensors” Technical Note.
Figure 6. SPI Read Data Fetch Command Structures
Two Byte Data Readout
Data Byte 1
MISO
Data Byte 2
S1 S0 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Status
Bridge Data [13:8]
Bridge Data [7:0]
SCLK
SS
Three Byte Data Readout
Data Byte 1
MISO
Data Byte 2
Data Byte 3
S1 S0 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 T10 T9 T8 T7 T6 T5 T4 T3
Status
Bridge Data [13:8]
Bridge Data [7:0]
Temperature Data [10:3]
Data Byte 2
Data Byte 3
SCLK
SS
Four Byte Data Readout
Data Byte 1
MISO
Data Byte 4
S1 S0 B13 B12 B11 B10 B9 B8 B7 B6 B4 B3 B2 B1 B0 B0 T10 T9 T8 T7 T6 T5 T4 T3 T2 T1 T0 X X X X X
Status
Bridge Data [13:8]
Bridge Data [7:0]
Temperature Data [10:3]
Temperature Data [2:0]
SCLK
SS
Bits generated by master
Bits generated by slave (sensor)
Honeywell • Sensing and Control
3
Technical Note
Sleep Mode for Use with Honeywell Digital Pressure Sensors:
ASDX Series, APB Series, and Trustability® HSC, SSC Series
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