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ISL22446UFV20Z Folha de dados(PDF) 11 Page - Intersil Corporation |
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ISL22446UFV20Z Folha de dados(HTML) 11 Page - Intersil Corporation |
11 / 15 page 11 FN6181.2 September 9, 2009 The electronic switches on the device operate in a “make before break” mode when the wiper changes tap positions. When the device is powered down, the last value stored in IVRi will be maintained in the non-volatile memory. When power is restored, the contents of the IVRi is recalled and loaded into the corresponding WRi to set the wiper to the initial value. DCP Description Each DCP is implemented with a combination of resistor elements and CMOS switches. The physical ends of each DCP are equivalent to the fixed terminals of a mechanical potentiometer (RH and RL pins). The RW pin of each DCP is connected to intermediate nodes, and is equivalent to the wiper terminal of a mechanical potentiometer. The position of the wiper terminal within the DCP is controlled by volatile Wiper Register (WR). Each DCP has its own WR. When the WR of a DCP contains all zeroes (WR[6:0]= 00h), its wiper terminal (RW) is closest to its “Low” terminal (RL). When the WR register of a DCP contains all ones (WR[6:0]= 7Fh), its wiper terminal (RW) is closest to its “High” terminal (RH). As the value of the WR increases from all zeroes (0) to all ones (127 decimal), the wiper moves monotonically from the position closest to RL to the closest to RH. At the same time, the resistance between RW and RL increases monotonically, while the resistance between RH and RW decreases monotonically. While the ISL22446 is being powered up, all four WRs are reset to 40h (64 decimal), which locates RW roughly at the center between RL and RH. After the power supply voltage becomes large enough for reliable non-volatile memory reading, all WRs will be reload with the value stored in corresponding non-volatile Initial Value Registers (IVRs). The WRs can be read or written to directly using the SPI serial interface as described in the following sections. The SPI interface register address bits have to be set to 0000b, 0001b, 0010b or 0011b to access the WR of DCP0, DCP1, DCP2 or DCP3 respectively. The WRi and IVRi can be read or written to directly using the SPI serial interface as described in the following sections. Memory Description The ISL22446 contains seven non-volatile and five volatile 8-bit registers. The memory map of ISL22446 is shown in Table 1. The four non-volatile registers (IVRi) at address 0, 1, 2 and 3, contain initial wiper value and volatile registers (WRi) contain current wiper position. In addition, three non-volatile General Purpose registers from address 4 to address 6 are available. The non-volatile IVRi and volatile WRi registers are accessible with the same address. The Access Control Register (ACR) contains information and control bits described in Table 2. The VOL bit (ACR[7]) determines whether the access is to wiper registers WR or initial value registers IVR. If VOL bit is 0, the non-volatile IVR register is accessible. If VOL bit is 1, only the volatile WR is accessible. Note, value is written to IVR register also is written to the WR. The default value of this bit is 0. The SHDN bit (ACR[6]) disables or enables Shutdown mode. This bit is logically ANDed with SHDN pin. When this bit is 0, DCP is in Shutdown mode. Default value of SHDN bit is 1. The WIP bit (ACR[5]) is read only bit. It indicates that non- volatile write operation is in progress. The WIP bit can be read repeatedly after a non-volatile write to determine if the write has been completed. It is impossible to write to the IVRi, WRi or ACR while WIP bit is 1. Shutdown Mode The device can be put in Shutdown mode either by pulling the SHDN pin to GND or setting the SHDN bit in the ACR register to 0. The truth table for Shutdown mode is in Table 3. SPI Serial Interface The ISL22446 supports an SPI serial protocol, mode 0. The device is accessed via the SDI input and SDO output with data clocked in on the rising edge of SCK, and clocked out on the falling edge of SCK. CS must be LOW during communication with the ISL22446. SCK and CS lines are controlled by the host or master. The ISL22446 operates only as a slave device. TABLE 1. MEMORY MAP ADDRESS NON-VOLATILE VOLATILE 8— ACR 7 Reserved 6 5 4 General Purpose General Purpose General Purpose Not Available Not Available Not Available 3 2 1 0 IVR3 IVR2 IVR1 IVR0 WR3 WR2 WR1 WR0 TABLE 2. ACCESS CONTROL REGISTER (ACR) BIT # 7 6 5 432 1 0 Bit Name VOL SHDN WIP 000 0 0 TABLE 3. SHDN pin SHDN bit Mode High 1 Normal operation Low 1 Shutdown High 0 Shutdown Low 0 Shutdown TABLE 1. MEMORY MAP (Continued) ADDRESS NON-VOLATILE VOLATILE ISL22446 |
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