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X9520V20IZ-B Datasheet(PDF) 7 Page - Intersil Corporation |
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X9520V20IZ-B Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 29 page 7 FN8206.2 August 20, 2007 At both ends of each array and between each resistor segment there is a CMOS switch connected to the wiper (Rwx) output. Within each individual array, only one switch may be turned on at any one time. These switches are controlled by the Wiper Counter Register (WCR) (See Figure 6). The WCR is a volatile register. On power-up of the X9520, wiper position data is automatically loaded into the WCR from its associated Non Volatile Memory (NVM) Register. The table below shows the Initial Values of the DCP WCR’s before the contents of the NVM is loaded into the WCR. The data in the WCR is then decoded to select and enable one of the respective FET switches. A “make before break” sequence is used internally for the FET switches when the wiper is moved from one tap position to another. Hot Pluggability Figure 7 shows a typical waveform that the X9520 might experience in a Hot Pluggable situation. On power-up, V1/VCC applied to the X9520 may exhibit some amount of ringing, before it settles to the required value. The device is designed such that the wiper terminal (RWx) is recalled to the correct position (as per the last stored in the DCP NVM), when the voltage applied to V1/VCC exceeds VTRIP1 for a time exceeding tpurst (the Power-on Reset time, set in the CONSTAT Register - See “Control and Status Register” on page 12.). Therefore, if ttrans is defined as the time taken for V1/VCC to settle above VTRIP1 (Figure 7): then the desired wiper terminal position is recalled by (a maximum) time: ttrans + tpurst. It should be noted that ttrans is determined by system hot plug conditions. DCP Operations In total there are three operations that can be performed on any internal DCP structure: • DCP Nonvolatile Write • DCP Volatile Write • DCP Read A nonvolatile write to a DCP will change the “wiper position” by simultaneously writing new data to the associated WCR and NVM. Therefore, the new “wiper position” setting is recalled into the WCR after V1/VCC of the X9520 is powered down and then powered back up. A volatile write operation to a DCP however, changes the “wiper position” by writing new data to the associated WCR only. The contents of the associated NVM register remains unchanged. Therefore, when V1/VCC to the device is powered down then back up, the “wiper position” reverts to that last position written to the DCP using a nonvolatile write operation. Both volatile and nonvolatile write operations are executed using a three byte command sequence: (DCP) Slave Address Byte, Instruction Byte, followed by a Data Byte (See Figure 9). A DCP Read operation allows the user to “read out” the current “wiper position” of the DCP, as stored in the associated WCR. This operation is executed using the Random Address Read command sequence, consisting of the (DCP) Slave Address Byte followed by an Instruction Byte and the Slave Address Byte again (Refer to Figure 10.). Instruction Byte While the Slave Address Byte is used to select the DCP devices, an Instruction Byte is used to determine which DCP is being addressed. DCP INITIAL VALUES BEFORE RECALL R0/64 TAP VH/TAP = 63 R1/100 TAP VL/TAP = 0 R2/256 TAP VH/TAP = 255 FIGURE 7. DCP POWER t V1/VCC VTRIP1 V1/VCC (Max) tpurst MAXIMUM WIPER RECALL TIME 0 ttrans X9520 |
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