The AD5222 provides a dual channel， 128-position， digitally controlled variable-resistor （VR） device. This device performs the same electronic adjustment function as a potentiometer or variable resistor. These products were optimized for instrument and test equipment push-button applications. Choices between bandwidth or power dissipation are available as a result of the wide selection of end-to-end terminal resistance values. The AD5222 contains two fixed resistors with wiper contacts that tap the fixed resistor value at a point determined by a digitally controlled up/down counter. The resistance between the wiper and either end point of the fixed resistor provides a constant resistance step size that is equal to the end-to-end resistance divided by the number of positions （e.g.， RSTEP = 10 k?/128 = 78 ?）。 The variable resistor offers a true adjustable value of resistance， between Terminal A and the wiper， or Terminal B and the wiper. The fixed A-to-B terminal resistance of 10 k?， 50 k?， 100 k?， or 1 M? has a nominal temperature coefficient of –35 ppm/°C. The chip select CS， count CLK and U/D direction control inputs set the variable resistor position. The MODE determines whether both VRs are incremented together or independently. With MODE at logic zero， both wipers are incremented UP or DOWN without changing the relative settings between the wipers. Also， the relative ratio between the wipers is preserved if either wiper reaches the end of the resistor array. In the independent MODE （Logic 1） only the VR determined by the DACSEL pin is changed. DACSEL （Logic 0） changes RDAC 1. These inputs， which control the internal up/down counter， can be easily generated with mechanical or push-button switches （or other contact closure devices）。 This simple digital interface eliminates the need for microcontrollers in front panel interface designs. The AD5222 is available in the surface-mount （SO-14） package. For ultracompact solutions， selected models are available in the thin TSSOP-14 package. All parts are guaranteed to operate over the extended industrial temperature range of –40°C to +85°C. For 3-wire， SPI-compatible interface applications， see the AD5203/AD5204/AD5206， AD7376， and AD8400/AD8402/ AD8403 products.