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Specifications	Installation Instruction PK Template kfevans
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Technical Note I2C Communications with Honeywell Digital Output Pressure Sensors Sensing and Control 1.0 Introduction The I2C

Specifications	Installation Instruction PK Template kfevans
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Content	Technical Note I2C Communications with Honeywell Digital Output Pressure Sensors Sensing and Control 1.0 Introduction The I2C bus is a simple, serial 8-bit oriented computer bus for efficient I2C (Inter-IC) control. It provides good support for communication between different ICs across short circuit-board distances, such as interfacing microcontrollers with various low speed peripheral devices. For detailed specifications of the I2C protocol, see Version 2.1 (January 2000) of the I2C Bus Specification (source: NXP Semiconductor at (http://www.nxp.com/acrobat_download/literature/9398/393400 11.pdf). Each device connected to the bus is software addressable by a unique address and a simple master/slave relationship that exists at all times. The output stages of devices connected to the bus are designed around an open collector architecture. Because of this, pull-up resistors to +VDD must be provided on the bus. Both SDA and SCL are bidirectional lines, and it is important to system performance to match the capacitive loads on both lines. In addition, in accordance with the I2C specification, the maximum allowable capacitance on either line is 400 pF to ensure reliable edge transitions at 400 kHz clock speeds (Figure 1). When the bus is free, both lines are pulled up to +VDD. Data on the I2C-bus can be transferred at a rate up to 100 kbit/s in the standard-mode, or up to 400 kbit/s in the fast-mode. Figure 1. I2C Bus Configuration Master Slave 1Slave 2Slave 3 SCL (Serial Clock Line) SDL (Serial Data Line) Pull Up ResistorsRpRp +VDD 2.0 Data Transfer with I2C Output Pressure Sensors Honeywell’s digital output pressure sensors are designed to work as slaves and will therefore only respond to requests from a master device. Following the address and read bit from the master, Honeywell digital output pressure sensors are designed to output up to 4 bytes of data, depending on the sensor options and the needs of the application. In all cases, the first two data bytes are the compensated pressure output, along with sensor status bits. The third and fourth bytes are for optional compensated temperature output. 2.1 Sensor Address Each sensor is referenced on the bus by a 7 bit slave address. The default address for Honeywell Pressure sensors is 40 (28 hex). Other available standard addresses are: 56 (38 hex), 72 (48 hex), 88 (58 hex), 104 (68 hex), 120 (78 hex), 136 (88 hex) and 152 (98 hex). (Other custom values are available. Please contact Honeywell Customer Service with questions regarding custom slave addresses.) 2.2 Pressure Reading To read out a compensated pressure reading, the master generates a START condition and sends the sensor slave address followed by a read bit (shown in Figure 2). After the sensor generates an acknowledge, it will transmit up to 4 bytes of data – the first two bytes containing the compensated pressure output, and the second two bytes containing the optional compensated temperature output. The master must acknowledge the receipt of each byte, and can terminate the communication by sending a Not Acknowledge (NACK) bit followed by a stop bit after receiving both bytes of data as show in Figure 2. 2.3 Temperature Reading The optional corrected temperature data can be read out with either 8 bit or 11 bit resolution. By reading out the third byte of data from the sensor, the 8 bit compensated temperature value can be read. Further, by reading out the fourth byte of data, the complete 11 bit optional compensated temperature value can be read. The 8 bit value gives an approximate 0.8 C resolution, while the 11 bit value gives an approximate 0.1 C resolution. When reading the full 11 bit resolution temperature output, the 5 least significant bits of the 4th data byte are “Do Not Care” and should be ignored.
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Following Datasheets	i2c_comms_with_honeywell_airflow_sensors_tech_note_008210-3-en_final_16dec11 (4 pages) ia352hl (4 pages) iaa_iac (2 pages) iad (2 pages) iama (2 pages) IAMS01 (2 pages) IAMSVFR (15 pages) IAMS_Manual (41 pages) iba_ibc (2 pages) ibd (2 pages)
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