Abstract: A left zero fill circuit particularly suited for incorporation into non-buffered keypunch machines for providing a left zero fill capability thereto. The circuit provides a combination of registers and memory storage devices operable in an input mode to accept keypunch data, and in an output mode to punch the data onto a card in the proper locations within the field. The circuit further includes isolation means interposed in the interconnections between the keypunch machine and the left zero elements to isolate the power supplies and to allow the keypunch machine to be serviced in the normal manner, simply by switching the left zero fill circuit off.