A message-based memory system for Digital Signal Processor storage expansion has a shared memory device connected to a number of DSPs through a packet communication bus. The sheet-metal-type part has at least one slot passing through the sheet-metal-type part in an area adjacent to the through-opening. A test set for the hard to detect faults is generated by using an improved automatic test pattern generator. An expanded Hamming code based decoder is used for correcting errors occurring during transmission.