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AD7814ARM Fiches technique(PDF) 6 Page - Analog Devices |
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AD7814ARM Fiches technique(HTML) 6 Page - Analog Devices |
6 / 8 page REV. E AD7814 –6– Read Operation Figure 2 shows the timing diagram for a serial read from the AD7814. The CS line enables the SCLK input. Ten bits of data and a leading zero are transferred during a read operation. Read operations occur during streams of 16 clock pulses. The serial data is accessed in a number of bytes if 10 bits of data are being read. At the end of the read operation, the DOUT line remains in the state of the last bit of data clocked out of the AD7814 until CS returns high, at which time the DOUT line goes into three-state. Write Operation Figure 2 also shows the timing diagram for a serial write to the AD7814. The write operation takes place at the same time as the read operation. Data is clocked into the control register on the part on the rising edge of SCLK. Only the third bit in the data stream provides a user-controlled function. This third bit is the power-down bit which, when set to a 1, puts the AD7814 into shutdown mode. The first 2 bits of the data stream are “don’t cares” while all other bits in the data stream, other than the power-down bit, should be 0 to ensure correct operation of the AD7814. Data is loaded to the control register on the fif- teenth falling SCLK edge and the data takes effect at this time (i.e., if the part is programmed to go into shutdown, it does so at this point). If the CS is brought high before this fifteenth SCLK edge, the control register will not be loaded and the power-down status of the part will not change. MICROPROCESSOR INTERFACING The AD7814’s serial interface allows for easy interface to most microcomputers and microprocessors. Figures 3 through 6 show some typical interface circuits. The serial interface on the AD7814 consists of four wires: CS, DIN, DOUT, and SCLK. All interface circuits shown utilize all four interface lines. However, it is possible to operate the inter- face with three wires. If the application does not require the power-down facility offered by the AD7814, the DIN line can be tied permanently low. Thus, the interface can be operated from just three wires: SCLK, CS, and DOUT. The serial data transfer to and from the AD7814 requires a 16-bit read operation. Many 8-bit microcontrollers have 8-bit serial ports and this 16-bit data transfer is handled as two 8-bit transfers. Other microcontrollers and DSP processors transfer 16 bits of data in a serial data operation. CS SCLK DOUT DIN DON'T CARE DON'T CARE POWER- DOWN LEADING ZERO DB9 DB8 DB0 1 234 11 15 16 t1 t2 t3 t4 t5 t6 t7 t8 Figure 2. Serial Interface Timing Diagram AD7814 to MC68HC11 Interface Figure 3 shows an interface between the AD7814 and the MC68HC11 microcontroller. The MC68HC11 is configured in the master mode with its CPOL bit set to a logic one and its CPHA bit set to a logic one. When the MC68HC11 is config- ured like this, its SCLK line idles high between data transfers. Data is transferred to and from the AD7814 in two 8-bit serial data operations. The diagram shows the full (4-wire) interface. PC1 of the MC68HC11 is configured as an output and used to drive the CS input. AD7814* SCLK DOUT DIN CS MC68HC11* SCLK MISO MOSI PC1 *ADDITIONAL PINS OMITTED FOR CLARITY Figure 3. AD7814 to MC68HC11 Interface AD7814 to 8051 Interface An interface circuit between the AD7814 and the 8051 micro- controller is shown in Figure 4. The 8xC51 is configured in its Mode 0 serial interface mode. The serial clock line of the 8xC51 (on P3.1) idles high between data transfers. Data is transferred to and from the AD7814 in two 8-bit serial data operations. The AD7814 outputs the MSB of its data stream as the first valid bit while the 8xC51 expects the LSB first. Thus, the data read into the serial buffer needs to be rearranged before the correct data word from the AD7814 is available in the accumulator. In the example shown, the AD7814 is connected to the serial port of the 8051. Because the serial interface of the 8xC51 con- tains only one data line, the DIN line of the AD7814 is tied low in the interface example given in Figure 4. For applications that require the use of the power-down feature of the AD7814, the serial interface should be implemented using data port lines on the 8051. This allows a full-duplex serial interface to be implemented. The method involves ‘bit- banging’ a port line to generate a serial clock while using two other port lines to shift data in and out with the fourth port line connecting to CS. Port lines 1.0 through 1.3 (with P1.1 config- ured as an input) can be used to connect to SCLK, DOUT, DIN, and CS, respectively, to implement this scheme. |
Numéro de pièce similaire - AD7814ARM |
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Description similaire - AD7814ARM |
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