is not necessary for the operation the binary voltage input code which is input by voltage pulses representing digital 0 and 1 by programs input into the cpu 37 and the program memory the software instruction programs and the operating program are input the tool cpu 18 thus the programs are placed in the tool in a nonvolatile memory which will retain the programs independent of power to the cpu 18 during the inputting of the programs or at the completion of the input of the software the host cpu 37 executes a verify step which directs the cpu 18 to play back the input programs to the host cpu 37 this is accomplished by encoding the programs as a binary current code the binary current code is obtained by a transistor circuit 42 in which the current is varied to provide the pulse code from the i o circuit 21 externally of the tool a load resistor 44 detects the current changes which are in binary code and inputs the current code to the host computer 37 for a read out of the program or verification of the data the voltage code input is of course operated independently of the current code output this is accomplished by a circuit 46 which separates voltage and current signals the system thus provides a.