1. An apparatus for controlling digital devices comprising, interface buffer means for storing input signals from a digital device and for storing output signals for a digital device where said input and output signals are operands, memory means for storing a program of instructions including instructions for specifying said buffer means as a source of and as the destination of variable-field operands utilized in executing said instructions, interpreter means connected to said memory means to fetch instructions from said memory means and connected to said buffer means to fetch and store operands from and to said buffer means, said interpreter means including means for sequentially fetching instructions from said memory means, means for executing fetched instructions, and means for fetching and storing variable-field operands from and to said buffer means in the execution of instructions whereby said input signals from a digital device are interpreted under program control to produce output signals to control a digital device.