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AD5391 Datasheet(PDF) 26 Page - Analog Devices |
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AD5391 Datasheet(HTML) 26 Page - Analog Devices |
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26 / 44 page  AD5390/AD5391/AD5392 Data Sheet Rev. F | Page 26 of 44 Standalone Mode By connecting the daisy-chain enable (DCEN) pin low, stand- alone mode is enabled. The serial interface works with both a continuous and a noncontinuous serial clock. The first falling edge of SYNC starts the write cycle and resets a counter that counts the number of serial clocks to ensure that the correct number of bits is shifted into the serial shift register. Any further edges on SYNC (except for a falling edge) are ignored until 24 bits are clocked in. Once 24 bits have been shifted in, the SCLK is ignored. For another serial transfer to take place, the counter must be reset by the falling edge of SYNC. Daisy-Chain Mode For systems that contain several devices, the SDO pin can be used to daisy-chain the devices together. This daisy-chain mode can be useful in system diagnostics and for reducing the number of serial interface lines. By connecting the DCEN 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. For each device in the system, 24 clock pulses are required. Therefore, the total number of clock cycles must equal 24N where N is the total number of AD5390/AD5391/AD5392 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 SYNC is taken high before 24 clocks are clocked into the part, it is considered a bad frame and the data is discarded. The serial clock can be either a continuous or a gated clock. A continuous SCLK source can be used only if the SYNC can be 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 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 sequence. With R/W = 1, Bit A3 to Bit 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 care bits. During the next SPI write, the data appearing on the SDO output contains 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. The readback diagram in Figure 32 shows the readback sequence. For example, to read back the m register of Channel 0 on the AD5390/AD5391/AD5392, the following sequence should be implemented: First, write 0x404XXX to the AD5390/AD5391/AD5392 input register. This configures the AD5390/AD5391/AD5392 for read mode with the m register of Channel 0 selected. Note that all data bits, DB13 to DB0, are don’t care bits. Follow this with a second write, a NOP condition, and 0x000000. During this write, the data from the m register is clocked out on the DOUT line, that is, data clocked out contains the data from the m register in Bit DB13 to Bit DB0, and the top 10 bits con- tain 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, 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 32. Readback Operation |
Similar Part No. - AD5391_15 |
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Similar Description - AD5391_15 |
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