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AD5392BST-5 Datasheet(PDF) 27 Page - Analog Devices |
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AD5392BST-5 Datasheet(HTML) 27 Page - Analog Devices |
27 / 40 page AD5382 Rev. 0 | Page 27 of 40 Daisy-Chain Mode For systems that contain several devices, the SDO pin may be used to daisy-chain several devices together. This daisy-chain mode can be useful in system diagnostics and in reducing the number of serial interface lines. By connecting the DCEN (Daisy-Chain Enable) pin high, daisy- chain mode is enabled. The first falling edge of SYNC starts the write cycle. The SCLK is continuously applied to the input shift register when SYNC is low. If more than 24 clock pulses are applied, the data ripples out of the shift register and appears on the SDO line. This data is clocked out on the rising edge of SCLK and is valid on the falling edge. By connecting the SDO of the first device to the DIN input on the next device in the chain, a multidevice interface is constructed. Twenty-four clock pulses are required for each device in the system. Therefore, the total number of clock cycles must equal 24N, where N is the total number of AD538x devices in the chain. When the serial transfer to all devices is complete, SYNC is taken high. This latches the input data in each device in the daisy-chain and prevents any further data from being clocked into the input shift register. If the SYNC is taken high before 24 clocks are clocked into the part, this is considered a bad frame and the data is discarded. The serial clock may be either a continuous or a gated clock. A continuous SCLK source can only be used if it can be arranged that SYNC is held low for the correct number of clock cycles. In gated clock mode, a burst clock containing the exact number of clock cycles must be used and SYNC must be taken high after the final clock to latch the data. Readback Mode Readback mode is invoked by setting the R/W bit = 1 in the serial input register write. With R/W = 1, Bits A4 to A0, in association with Bits REG1 and REG0, select the register to be read. The remaining data bits in the write sequence are don’t cares. During the next SPI write, the data appearing on the SDO output will contain the data from the previously addressed register. For a read of a single register, the NOP command can be used in clocking out the data from the selected register on SDO. Figure 30 shows the readback sequence. For example, to read back the M register of channel 0 on the AD5382, the following sequence should be implemented. First, write 0x404XXX to the AD5382 input register. This configures the AD5382 for read mode with the m register of Channel 0 selected. Note that data bits DB13 to DB0 are don’t cares. Follow this with a second write, a NOP condition, 0x000000. During this write, the data from the m register is clocked out on the DOUT line, i.e., data clocked out will contain the data from the m register in Bits DB13 to DB0, and the top 10 bits contain the address information as previously written. In readback mode, the SYNC signal must frame the data. Data is clocked out on the rising edge of SCLK and is valid on the falling edge of the SCLK signal. If the SCLK idles high between the write and read operations of a readback operation, the first bit of data is clocked out on the falling edge of SYNC. 24 48 SCLK SYNC DIN SDO UNDEFINED SELECTED REGISTER DATA CLOCKED OUT NOP CONDITION INPUT WORD SPECIFIES REGISTER TO BE READ DB23 DB0 DB0 DB23 DB23 DB0 DB0 DB23 Figure 30. Serial Readback Operation |
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