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AD7889 Scheda tecnica(PDF) 32 Page - Analog Devices |
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AD7889 Scheda tecnica(HTML) 32 Page - Analog Devices |
32 / 40 page AD7879/AD7889 Data Sheet Rev. D | Page 32 of 40 SYNCHRONIZING THE AD7879/AD7889 TO THE HOST CPU The two methods for synchronizing the AD7879/AD7889 to the host CPU are slave mode (in which the mode bits are set to 01 or 10) and master mode (in which the mode bits set to 11). In master mode (ADC mode bits = 11), PENIRQ can be used as an interrupt to the host. When PENIRQ goes low to indicate that the screen has been touched, the host is awakened. The host can then program the AD7879/AD7889 to convert in any mode and read the results after the conversions are completed. In master mode, INT or DAV can also be used as an interrupt to the host. The host must first define a conversion sequence in Control Register 3, initialize the AD7879/AD7889 in Mode 11, and enable INT or DAV using Bit 15 in Control Register 1 and Bit 13 in Control Register 3. The host can then enter sleep mode to conserve power. The wake-up on touch feature of the AD7879/ AD7889 is active in this mode; therefore, when the screen is touched, the programmed sequence of conversions automatically begins. When the INT or DAV signal is asserted, the host reads the new data available in the AD7879/AD7889 result registers and returns to sleep mode. This method can significantly reduce the load on the host. Figure 38 shows how the PENIRQ circuit is enabled. The wake-up on touch circuit and the PENIRQ circuit are enabled only in master mode (ADC mode = 11). In slave mode, the PENIRQ/INT/DAV pin can output only INT or DAV signals. ADC MODE = 11? MASTER MODE 0 1 0 1 DAV (END OF CONVERSION SEQUENCE) INT (GPIO ALERT/OUT OF LIMITS) INT/DAV/GPIO ALERT TOUCH SCREEN TOUCHED CONTROL REGISTER 3 BIT 13 CONTROL REGISTER 1 BIT 15 PENIRQ/INT/DAV PIN TO THE DIGITAL CORE ENABLE WAKE-UP ON TOUCH ENABLE PENIRQ DETECTION CIRCUIT TOUCH SCREEN TOUCHED YES YES Figure 38. Master Mode Operation |
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