The ISO121x devices provide an output-enable pin on the controller side (EN). Setting the EN pin to 0 causes the output buffers to be in the high-impedance state. This feature can be used to multiplex the outputs of multiple ISO121x devices on the same host-controller input, reducing the number of pins on the host controller.
In the example shown in Figure 25, two sets of 8-channel inputs are multiplexed, reducing the number of input pins required on the controller from 16 to 10. Similarly, if four sets of 8-channel inputs are multiplexed, the number of pins on the controller is reduced from 32 to 12.