A decoder (7) decodes a channel control word (3) for selecting one of the input channels (1, CHO-CH7) by producing the signals (S0-S7). The multiplexer (2) selects one of the analogue-input connections (1) corresponding to the signal (S0, S1, ... S7) for transmitting the analogue signal to the converting device (10). The external channel control unit (5, 9) reacts to an external channel selecting signal (6) for changing the channel control word passing from outside to the converting device and controlling the multiplexer.
