The AD5207 provides dual channel， 256-position， digitally controlled variable resistor （VR） devices that perform the same electronic adjustment function as a potentiometer or variable resistor. Each channel of the AD5207 contains a fixed resistor with a wiper contact that taps the fixed resistor value at a point determined by a digital code loaded into the SPI-compatible serial-input register. The resistance between the wiper and either end point of the fixed resistor varies linearly with respect to the digital code transferred into the VR latch. The variable resistor offers a completely programmable value of resistance， between the A Terminal and the wiper or the B Terminal and the wiper. The fixed A-to-B terminal resistance of 10 k?， 50 k? or 100 k? has a ±1% channel-to-channel matching tolerance with a nominal temperature coefficient of 500 ppm/°C. A unique switching circuit minimizes the high glitch inherent in traditional switched resistor designs and avoids any make-before-break or breakbefore-make operation. Each VR has its own VR latch， which holds its programmed resistance value. These VR latches are updated from an internal serial-to-parallel shift register， which is loaded from a standard 3-wire serial-input digital interface. Ten bits， to make up the data word， are required and clocked into the serial input register. The first two bits are address bits. The following eight bits are the data bits that represent the 256 steps of the resistance value. The reason for two address bits instead of one is to be compatible with similar products such as AD8402 so that drop-in replacement is possible. The address bit determines the corresponding VR latch to be loaded with the data bits during the returned positive edge of CS strobe. A serial data output pin at the opposite end of the serial register allows simple daisy chaining in multiple VR applications without additional external decoding logic. An internal reset block will force the wiper to the midscale position during every power-up condition. The SHDN pin forces an open circuit on the A Terminal and at the same time shorts the wiper to the B Terminal， achieving a microwatt power shutdown state. When SHDN is returned to logic high， the previous latch settings put the wiper in the same resistance setting prior to shutdown. The digital interface remains active during shutdown; code changes can be made to produce new wiper positions when the device is resumed from shutdown. The AD5207 is available in 1.1 mm thin TSSOP-14 package， which is suitable for PCMCIA applications. All parts are guaranteed to operate over the extended industrial temperature range of –40°C to +125°C