Installation Instruction PK Template kfevans

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

Specifications	Installation Instruction PK Template kfevans
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Content	Technical Note I2C Communications with Honeywell Digital Airflow 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 I2C Bus Specification Version 2.1 January 2000. Source: NXP Semiconductor at http://www.nxp.com/acrobat_download/literature/9398/393400 11.pdf. (Note: this link is controlled by NXP Semiconductor and is subject to change by them.) 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 SCL and SDA 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 (see 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 1 Slave 2 Slave 3 SCL (Serial Clock Line) SDA (Serial Data Line) Pull-Up ResistorsRSCLRSDA +VDD 2.0 Sensor Address Each I2C digital sensor is referenced on the bus by a 7-bit slave address. The I2C default address is 0x49; however, the address is selectable according to the Nomenclature and Order Guide in the Honeywell Zephyr™ Digital Airflow Sensors: HAF Series- High Accuracy product data sheet. (Other custom values are available. Please contact Honeywell Customer Service if there are questions regarding custom slave addresses.) 3.0 Digital Flow Reading Honeywell’s digital output airflow sensors are designed to work as slaves and will therefore only respond to requests from a master device. The sensors operate as a slave-only and the READ command structure is shown in Figure 2. The sensors report the 0x00 or “data not ready” status until after a start-up time of ~17 ms. The first two consecutive READ commands that respond with non-zero valid data will provide the contents of two 16-bit registers with serial number information with the following format. Serial Number Format: Register 0 [15:14] status in manufacturing [reserved – don’t care ‘XX’] [13:9] production year [8:0] production day of year Register 1 [15:12] Model number of DUT [11:0] Sequential DUT number for production day Figure 2. Standard I2C READ Command and Word Structure READ (Slave Returning Data to the Master) Start bit S65430211A7653210A643210NS S S A 0 2 2 Stop bit Acknowledge Slave address bit (example: bit 2) Response bit (example: bit 2) Read/write (example: write) 457 Address ByteResponse ByteResponse Byte Wait for Slave ACKMaster ACKMaster NACK The sensor is asynchronous at start-up and will wait to supply the sequential serial number values on the first two READ commands. After the serial number registers are read in succession, the sensor will then begin repeating 14-bit calibrated flow sensor output values updated every 1 ms (I2C 16-bit word including two leading zero bits = ’00’ specifying calibrated flow data packet). Table 1 shows the initial start-up sequence and subsequent data transfers of the sensor after power is applied.
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Following Datasheets	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) IBL_WEB_BROCHURE_REVB (4 pages)
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