The MAX4135 provides TTL/CMOS-compatible, digital control pins (SEL1SEL6) to enable or disable each amplifier output. When the SEL_ input is low, the amplifier is enabled; when it is high, the amplifier is disabled. The EV kit uses a DIP switch (SW1) to manually enable/disable outputs. When a switch is on, the SEL_ pin is connected to ground, and the corresponding amplifier is enabled. When a switch is off, the SEL_ pin is connected to +5V through a 100k pull-up resistor, and the corresponding amplifier is disabled. To use an external controller, set the desired S EL_ switch(es) to on and connect the external controller to the pad(s) labeled SEL_.