3.2 ACCUMULATOR

The accumulator is simply a register that will store the result of the operation performed. Nevertheless, the accumulator was designed as a separate unit because it is supposed to support the scan mode operation. In brief, the accumulator operates in two modes: the normal mode and the scan mode. When it is in the normal mode it just passes the input to the output. But in the scan mode it becomes a shift register. So eight 2-1 multiplexers were used to select between the normal inputs and the shift inputs with  the select signal being scanmode Figure three shows the block diagram for the accumulator.