CAT5136, CAT5137, and CAT5138 are a family of digital POTs operating like mechanical potentiometers in various configurations. The tap points between the 127 equal resistive elements are connected to the wiper output via CMOS switches. The switches are controlled by a 7-bit Wiper Control Register (WCR) via the I2C serial bus. CAT5136 is configured as a variable resistor. CAT5137 and CAT5138 are resistive voltage dividers, with one terminal of the potentiometer connected to GND. CAT5137 and CAT5138 have different device IDs, which makes it possible to use both on the same I2C bus. Upon power-up, the WCR is set to mid-scale (1000000).