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AD7147A Fiches technique(PDF) 28 Page - Analog Devices |
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AD7147A Fiches technique(HTML) 28 Page - Analog Devices |
28 / 69 page AD7147A Rev. B | Page 27 of 68 INTERRUPT OUTPUT SENSOR-TOUCH INTERRUPT The AD7147A has an interrupt output that triggers an interrupt service routine on the host processor. The INT signal is on Pin A1 and is an open-drain output. There are three types of interrupt events on the AD7147A: a CDC conversion-complete interrupt, a sensor-touch interrupt, and a GPIO interrupt. Each interrupt has enable and status registers. The conversion-complete and sensor-touch (sensor-activation) interrupts can be enabled on a per-conversion-stage basis. The status registers indicate what type of interrupt triggered the INT pin. Status registers are cleared, and the INT signal is reset high during a read operation. The signal returns high as soon as the read address has been set up. The sensor-touch interrupt mode is implemented when the host processor requires an interrupt only when a sensor is contacted. Configuring the AD7147A into this mode results in the interrupt being asserted when the user makes contact with the sensor and again when the user stops touching the sensor. The second interrupt is required to alert the host processor that the user is no longer contacting the sensor. The registers located at Address 0x005 and Address 0x006 are used to enable the interrupt output for each stage. The registers located at Address 0x008 and Address 0x009 are used to read back the interrupt status for each stage. CDC CONVERSION-COMPLETE INTERRUPT The AD7147A interrupt signal asserts low to indicate the comple- tion of a conversion stage and that new conversion result data is available in the registers. Figure 39 shows the interrupt output timing during contact with one of the sensors connected to STAGE0 while operating in the sensor-touch interrupt mode. For a low limit configuration, the interrupt output is asserted as soon as the sensor is contacted and again after the user has stopped touching the sensor. (Note that the interrupt output remains low until the host processor reads back the interrupt status registers located at Address 0x008 and Address 0x009.) The interrupt can be independently enabled for each conversion stage. Each conversion-stage-complete interrupt can be enabled via the STAGE_COMPLETE_INT_ENABLE register (Address 0x007). This register has a bit that corresponds to each conversion stage. Setting this bit to 1 enables the interrupt for that stage. Clearing this bit to 0 disables the conversion-complete interrupt for that stage. The interrupt output is asserted when there is a change in the interrupt status bits. This can indicate that a user is touching the sensor(s) for the first time, the number of sensors being touched has changed, or the user is no longer touching the sensor(s). Reading the status bits in the interrupt status register shows the current sensor activations. The AD7147A interrupt should be enabled only for the last stage in a conversion sequence. For example, if there are five conversion stages, only the conversion-complete interrupt for STAGE4 is enabled. Therefore, INT asserts only when all five conversion stages are complete and the host can read new data from all five result registers. The interrupt is cleared by reading the STAGE_COMPLETE_INT_STATUS register located at Address 0x00A. 4 2 CONVERSION STAGE SERIAL READBACK INT OUTPUT 3 1 STAGE1 STAGE0 FINGER ON SENSOR FINGER OFF SENSOR 1USER TOUCHING SENSOR. 2ADDRESS 0x008 IS READ BACK TO CLEAR INTERRUPT. 3USER STOPS TOUCHING SENSOR. 4ADDRESS 0x008 IS READ BACK TO CLEAR INTERRUPT. Register 0x00A is the conversion-complete interrupt status register. Each bit in this register corresponds to a conversion stage. If a bit is set, it means that the conversion-complete interrupt for the corresponding stage was triggered. This register is cleared upon a read if the underlying condition that triggered the interrupt is not present. Figure 39. Example of Sensor-Touch Interrupt |
Numéro de pièce similaire - AD7147A |
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Description similaire - AD7147A |
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