so that the control document always remains on the top of the stack of advancing documents such a transport deck is used in the insertamax iii mail inserter available from pitney bowes inc of stamford ct however it should be understood that the transport deck may be of other types such as that used in the insertamax ii mail inserter available from pitney bowes inc of stamford ct or the transport deck disclosed in u s pat no 3 934 867 issued on jan 27 1976 and assigned to pitney bowes inc the collated stack of documents is inserted in an envelope at the envelope station and transported to conventional accessory document handling stations 34 of the type previously described first envelope is sealed or not sealed as desired by a sealing unit the necessary postage is then provided by a postage meter such as for example pitney bowes inc model no 4255 postage meter the envelopes may then be transported to a single or multi level stacker referring to fig2 a through 2g the accessory interface circuit is illustrated generally as 32 the accessory interface circuit 32 includes an accessory interface microcomputer 35 which may be a model 8742 available from intel corporation address signals are received from the supervisory control circuit 20 over address lines 33 and inputted to the chip select port of the microcomputer 35 from the output of an or gate 36 an address receive acknowledge signal is.