The invention relates to a programmable controller comprising modules (3) connecting to each other by way of a backplane bus (1) which is mounted in a substantially C-shaped, electrically conductive mounting rack (2). Consequently, said backplane bus (1) is enclosed by the mounting rack (2) on three sides, the modules (3) being mounted on the mounting rack (2) with the result that they are mechanically supported thereon, are electrically connected to the backplane bus (1) and have a direct earth connection to said mounting rack (2).