Abstract: Duplicated circuit arrangement comprising a main processor (30) and its P bit data bus (44), and two identical redundant devices (21:22), each device is comprised of a processing element (23;35) performing the same task in parallel on a P bits word, and send/receive circuits (24,25;36,37) controlled by the main processor through lines (SR11 to SR22) to transmit said word to and from said main processor. For each device, the send/receive circuits are split into two parts. Send/receive circuit of the first device (21) is split in two parts (24, 25); the first part (24) handles the P/2 Most Significant Bits (MSB's) and the second part (25) handles the P/2 Less Significant Bits (LSB's). In normal operation, during the transmission step, only the first part (24) is allowed to send bits on one half (33) of the data bus (44).