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X9420YSM-2.7 Datasheet(PDF) 3 Page - Xicor Inc. |
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X9420YSM-2.7 Datasheet(HTML) 3 Page - Xicor Inc. |
3 / 20 page X9420 Characteristics subject to change without notice. 3 of 20 REV 1.1.6 7/30/02 www.xicor.com PIN NAMES PRINCIPLES OF OPERATION The X9420 is a highly integrated microcircuit incorporating a resistor array and associated registers and counter and the serial interface logic providing direct communication between the host and the XDCP potentiometer. Serial Interface The X9420 supports the SPI interface hardware conventions. The device is accessed via the SI input with data clocked in on the rising SCK. CS must be LOW and the HOLD and WP pins must be HIGH during the entire operation. The SO and SI pins can be connected together, since they have three state outputs. This can help to reduce system pin count. Array Description The X9420 is comprised of one resistor array containing 63 discrete resistive segments that are connected in series. The physical ends of each array are equivalent to the fixed terminals of a mechanical potentiometer (VH/RH and VL/RL inputs). At both ends of the array and between each resistor segment is a CMOS switch connected to the wiper (VW/RW) output. Within the individual array only one switch may be turned on at a time. These switches are controlled by a Wiper Counter Register (WCR). The six bits of the WCR are decoded to select, and enable, one of sixty-four switches. The block diagram of the potentiometer is shown in Figure 1. Wiper Counter Register (WCR) The X9420 contains a Wiper Counter Register. The WCR can be envisioned as a 6-bit parallel and serial load counter with its outputs decoded to select one of sixty-four switches along its resistor array. The contents of the WCR can be altered in four ways: it may be written directly by the host via the Write Wiper Counter Register instruction (serial load); it may be written indirectly by transferring the contents of one of four associated data registers via the XFR Data Register instruction (parallel load); it can be modified one step at a time by the Increment/ Decrement instruction. Finally, it is loaded with the contents of its data register zero (DR0) upon power-up. The Wiper Counter Register is a volatile register; that is, its contents are lost when the X9420 is powered- down. Although the register is automatically loaded with the value in DR0 upon power-up, this may be different from the value present at power-down. Data Registers The potentiometer has four 6-bit nonvolatile Data Registers. These can be read or written directly by the host. Data can also be transferred between any of the four Data Registers and the WCR. It should be noted all operations changing data in one of the Data Registers is a nonvolatile operation and will take a maximum of 10ms. If the application does not require storage of multiple settings for the potentiometer, the Data Registers can be used as regular memory locations for system parameters or user preference data. Register Descriptions Table 1. Data Registers, (6-bit), Nonvolatile There are four 6-bit Data Registers associated with the potentiometer. – {D5~D0}: These bits are for general purpose Nonvol- atile data storage or for storage of up to four different wiper values. Table 2. Wiper Counter Register, (6-bit), Volatile – {WP5~WP0}: These bits specify the wiper position of the potentiometer. Symbol Description SCK Serial Clock SI, SO Serial Data A0 Device Address VH/RH, VL/RL Potentiometer Pins (terminal equivalent) VW/RW Potentiometer Pins (wiper equivalent) WP Hardware Write Protection HOLD Serial Communication Pause V+,V- Analog Supplies VCC System Supply Voltage VSS System Ground NC No Connection 0 0 D5 D4 D3 D2 D1 D0 (MSB) (LSB) 0 0 WP5 WP4 WP3 WP2 WP1 WP0 (MSB) (LSB) |
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