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AD7776 датащи(PDF) 6 Page - Analog Devices |
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AD7776 датащи(HTML) 6 Page - Analog Devices |
6 / 12 page AD7776/AD7777/AD7778 –6– REV. 0 CR6: Determines whether operation is on a single channel or simultaneous sampling on two channels. Location CR6 is a “don’t care” for the AD7776. CR6 Function 0 Single channel operation. Channel select address is contained in locations CR0–CR2. 1 Two channels simultaneously sampled and sequentially converted. Channel select addresses contained in locations CR0–CR2 and CR3–CR5. CR7: Determines whether the device is in the normal operating mode or in the half-scale test mode. CR7 Function 0 Normal Operating Mode 1 Half-Scale Test Mode In the half-scale test mode REFIN is internally connected as an analog input(s). In this mode locations CR0–CR2 and CR3– CR5 are all “don’t cares” since it is REFIN which will be con- verted. For the AD7777 and AD7778, the contents of location CR6 still determine whether a single or a double conversion is carried out on the REFIN level. CR8: Determines whether the device is in the normal operating mode or in the powerdown mode. CR8 Function 0 Normal Operating Mode 1 Powerdown Mode In the powerdown mode all linear circuitry is turned off and the REFOUT output is weakly (5 k Ω) pulled to AGND. The input impedance of the analog inputs and of the REFIN input re- mains the same in either normal mode or powerdown mode. See under Circuit Description—Powerdown Mode. CR9: Determines whether BUSY/INT output flag goes low and remains low during conversion(s) or else goes low and remains low after the conversion(s) is (are) complete. CR9 BUSY/INT Functionality 0 Output goes low and remains low during conversion(s). 1 Output goes low and remains low after conversion(s) is (are) complete. ADC Conversion Start Timing Figure 6 shows the operating waveforms for the start of a con- version cycle. On the rising edge of WR, the conversion cycle starts with the acquisition and tracking of the selected ADC channel, AIN1–8. The analog input voltage is held 40 ns (typi- cally) after the first rising edge of CLKIN following four com- plete CLKIN cycles. If tD in Figure 6 is greater than 12 ns, the falling edge of CLKIN as shown will be seen as the first falling clock edge. If tD is less than 12 ns, the first falling clock edge to be recognized will not occur until one cycle later. Following the “hold” on the analog input(s), two complete CLKIN cycles are allowed for settling purposes before the MSB decision is made. The actual decision point occurs approximately 40 ns after the rising edge of CLKIN as shown in Figure 6. A further two CLKIN cycles are allowed for the second MSB decision. The succeeding bit decisions are made approximately 40 ns after each rising edge of CLKIN until the conversion is complete. At the end of conversion, if a single conversion has been requested (CR6 = 0), the BUSY/INT line changes CONTROL REGISTER The control register is 10-bits wide and can only be written to. On power-on, all locations in the control register are automati- cally loaded with 0s. For the single channel AD7776, locations CR0 to CR6 of the control register are “don’t cares.” For the quad channel AD7777, locations CR2 and CR5 are “don’t cares.” Individual bit functions are described below. CR0–CR2: Channel Address Locations. Determines which channel will be selected and converted for single channel operation. For si- multaneous sampling operation CR0–CR2 holds the address of one of the two channels to be sampled. AD7776 CR2 CR1 CR0 Function X* X X Select AIN1 *X = Don’t Care AD7777 CR2 CR1 CR0 Function X* 0 0 Select AIN1 X 0 1 Select AIN2 X 1 0 Select AIN3 X 1 1 Select AIN4 *X = Don’t Care AD7778 CR2 CR1 CR0 Function 0 0 0 Select AIN1 0 0 1 Select AIN2 0 1 0 Select AIN3 0 1 1 Select AIN4 1 0 0 Select AIN5 1 0 1 Select AIN6 1 1 0 Select AIN7 1 1 1 Select AIN8 CR3–CR5: Channel Address Locations. Only applicable for simul- taneous sampling with the AD7777 or AD7778 when CR3–CR5 holds the address of the second channel to be sampled. AD7777 CR5 CR4 CR3 Function X* 0 0 Select AIN1 X 0 1 Select AIN2 X 1 0 Select AIN3 X 1 1 Select AIN4 *X = Don’t Care AD7778 CR5 CR4 CR3 Function 0 0 0 Select AIN1 0 0 1 Select AIN2 0 1 0 Select AIN3 0 1 1 Select AIN4 1 0 0 Select AIN5 1 0 1 Select AIN6 1 1 0 Select AIN7 1 1 1 Select AIN8 |
Аналогичный номер детали - AD7776 |
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Аналогичное описание - AD7776 |
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