A data transmission device forwards data that have been received from a first device, intended for a second device, to the second device. The data transmission device is distinguished in that it has connections for connecting at least two data buses and can output data received by a first data bus either onto the same data bus or onto another data bus immediately or later. Therefore, the data transmission device can be used selectively, alternately or simultaneously as a DMA controller and a bus bridge. It also has additional functions unrelated to DMA controllers and bus bridges.