DS-0355 Datasheet, PDF (7/16 Pages) All Sensors Corporation – DLH Series Low Voltage Digital Pressure Sensors

I2C Interface (Cont’d)
I2C Bus Communications Overview
The I2C interface uses a set of signal sequences for communication. The following is a description of the sup-
ported sequences and their associated mnemonics. Refer to Figure 3 for the associated usage of the following
signal sequences.
Bus not Busy (I): During idle periods both data line (SDA) and clock line (SCL) remain HIGH.
START condition (ST): A HIGH to LOW transition of SDA line while the clock (SCL) is HIGH is interpreted as
START condition. START conditions are always set by the master. Each initial request for a pressure value has to
begin with a START condition.
Slave address (An): The I²C-bus requires a unique address for each device. The DLH sensor has a preconfigured
slave address (see specification table on Page 3). After setting a START condition the master sends the address
byte containing the 7 bit sensor address followed by a data direction bit (R/W). A “0” indicates a transmission
from master to slave (WRITE), a “1” indicates a device-to master request (READ).
Acknowledge (A or N): Data is transferred in units of 8 bits (1 byte) at a time, MSB first. Each data-receiving
device, whether master or slave, is required to pull the data line LOW to acknowledge receipt of the data. The
Master must generate an extra clock pulse for this purpose. If the receiver does not pull the data line down, a
NACK condition exists, and the slave transmitter becomes inactive. The master determines whether to send
the last command again or to set the STOP condition, ending the transfer.
DATA valid (Dn): State of data line represents valid data when, after a 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 data bit.
STOP condition (P): LOW to HIGH transition of the SDA line while clock (SCL) is HIGH indicates a STOP con-
dition. STOP conditions are always generated by the master.
Figure 3 - I2C Communication Diagram
1. Measurement Commands: Start-Single ( to start reading of single sample):
Start-Single
Start-Average2
Start-Average4
Start-Average8
Start-Average16
C23…C16: 0xAA
C23…C16: 0xAC
C23…C16: 0xAD
C23…C16: 0xAE
C23…C16: 0xAF
Set by bus master:
Set by sensor:
I ST A6 A5 A4 A3 A2 A1 A0 W C23 … C16
A
A
0x00
0x00
C15 … C8
C7 … C0
SP I
A
N
2. Status Read :
Set by bus master:
Set by sensor:
I ST A6 A5 A4 A3 A2 A1 A0 R
N SP I
A S7 … S0
3. Data Read:
Set by bus master:
Set by sensor:
I ST A6 A5 A4 A3 A2 A1 A0 R
A
A
A
A
A
A
N SP I
A S7 … S0
P23 … P16
P15 … P8 P7 … P0 T23 … T16
T15 … T8
T7 … T0
Bus states:
Idle:
I
Start:
ST
Stop:
SP
Ack:
A
Nack:
N
“Read” bit (1): R
“Write” bit (0): W
Sensor Address:
A6 … A0
Default: 0x29
Command Bits:
C23 … C0
Data bits:
Status:
Pressure data:
Temperature data:
S7 … S0
P23 … P0
T23 … T0
All Sensors
DS-0355 Rev A
Page 7