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AD5260 датащи(PDF) 10 Page - Analog Devices |
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AD5260 датащи(HTML) 10 Page - Analog Devices |
10 / 20 page REV. 0 –10– AD5232 Also the left shift commands were modified so that if the data in the RDAC register is greater than or equal to midscale and the data is left shifted then the data in the RDAC register is set to full-scale. This makes the left shift function as close to ideally logarithmic as is possible. The right shift #4 and #5 commands will be ideal only if the LSB is zero (i.e., ideal logarithmic–no error). If the LSB is a one then the right shift function generates a linear half LSB error, which translates to a code dependent logarithmic error for odd codes only as shown in the attached plots, (see Figure 5). The plot shows the errors of the odd codes for the AD5232. 0000 0000 0000 0001 0000 0010 0000 0100 0000 1000 0001 0000 0010 0000 0100 0000 1000 0000 1111 1111 1111 1111 LEFT SHIFT 1111 1111 0111 1111 0011 1111 0001 1111 0000 1111 0000 0111 0000 0011 0000 0001 0000 0000 0000 0000 0000 0000 RIGHT SHIFT LEFT SHIFT (+6 dB) RIGHT SHIFT (–6 dB) Figure 6. Detail Left and Right Shift Function for the 8-Bit AD5232 Actual conformance to a logarithmic curve between the data contents in the RDAC register and the wiper position for each Right Shift #4 and #5 command execution contains an error only for the odd codes. Even codes are ideal except zero right shift or greater than half-scale left shift. The graph in Figure 7 shows plots of Log_Error [i.e., 20 × log 10 (error/code)]. For example, code 3 Log_Error = 20 × log 10 (0.5/3) = –15.56 dB, which is the worst case. The plot of Log_Error is more signifi- cant at the lower codes. CODE, FROM 1 TO 255 BY 2 20 40 60 80 100 0 120 140 160 180 200 220 240 260 0 –10 –20 –30 –40 –50 –60 LOG_ERROR (CODE) FOR 8-BIT Figure 7. Plot of Log_Error Conformance for Odd Codes Only (Even Codes Are Ideal) ADVANCED CONTROL MODES The AD5232 digital potentiometer contains a set of user program- ming features to address the wide applications available to these universal adjustment devices. Key programming features include: Independently Programmable Read and Write to all registers. • Simultaneous refresh of all RDAC wiper registers from corresponding internal EEMEM registers. • Increment and Decrement instructions for each RDAC wiper register. • Left and right bit shift of all RDAC wiper registers to achieve 6 dB level changes. • Nonvolatile storage of the present scratch pad RDAC register values into the corresponding EEMEM register. • Fourteen extra bytes of user-addressable electrical-erasable memory. Increment and Decrement Commands The increment and decrement commands (#14, #15, #6, #7) are useful for the basic servo adjustment application. This com- mand simplifies microcontroller software coding by eliminating the need to perform a readback of the current wiper position, then add one to the register contents using the microcontroller’s adder. The microcontroller simply sends an increment command (#14) to the digital POT, which will automatically move the wiper to the next resistance segment position. The master incre- ment command (#15) will move all POT wipers by one position from their present position to the next resistor segment position. The direction of movement is referenced to Terminal B. Thus each increment #15 command will move the wiper tap position farther away from Terminal B. Logarithmic Taper Mode Adjustment Programming instructions allow a decrement and an increment wiper position control by individual POT or in a ganged POT arrangement where both wiper positions are changed at the same time. These settings are activated by the 6 dB decrement and 6 dB increment instructions #4 and #5 and #12 and #13 respectively. For example, starting with the wiper connected to Terminal B executing nine increment instructions (#12) would move the wiper in +6 dB steps from the 0% of RBA (B terminal) position to the 100% of RBA position of the AD5232 8-Bit potentiometer. The 6 dB increment instruction doubles the value of the RDAC register contents each time the command is executed. When the wiper position is greater than midscale, the last 6 dB increment instruction will cause the wiper to go to the Full-Scale 255 code position. Any additional +6 dB instruction will no longer change the wiper position from full scale (RDAC register code = 255). Figure 6 illustrates the operation of the 6 dB shifting function on the individual RDAC register data bits for the 8-bit AD5232 example. Each line going down the table represents a successive shift operation. Very important: the left shift #12 and #13 com- mands were modified so that if the data in the RDAC register is equal to zero and the data is left shifted, it is then set to code 1. |
Аналогичный номер детали - AD5260 |
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Аналогичное описание - AD5260 |
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