Field of the Invention
The invention relates to a method and configuration for transmitting digital data, which is divided up into data frames of variable length, from a first data bus to a second data bus and controlled by a microprocessor.
The integrated services digital network (ISDN) provides each subscriber with access to two so-called B channels for communicating with other subscribers, as well as to a so-called D channel in order to interchange signaling for a desired connection with the ISDN. While the ISDN does not ensure any data protection for the subscribers when communicating on the B channels, the ISDN demands for the D channel data protection conforming to the requirements of Layer 2 of the international standardization organization/open systems interconnection (ISO-OSI) layer model. To this end, the high-level data link control (HDLC) protocol is used for the ISDN.
Hence, the terminals and network interface equipment for the ISDN are provided with HDLC control devices which check the data protection information for a received D-channel frame and add protection information to a D-channel frame which is to be transmitted. The applicant markets such control devices under the product name PEB 2070 which is an integrated semiconductor component.
An incoming D-channel signal is supplied to an HDLC receiver logic unit, which checks the protection information for the received D-channel signal. An output signal from the HDLC receiver logic unit is supplied to a first-in first-out (FIFO) memory of a fixed size. A microprocessor removes the data contained in the FIFO memory from the latter in blocks. In the transmission direction, the microprocessor writes data to an FIFO transmission memory in blocks. An HDLC transmission logic unit removes the data contained in the FIFO transmission memory from the latter, adds protection information to a complete D-channel frame and outputs the D-channel signal thus obtained.