Time multiplexed signal communications between a host computer and subordinate data processing terminals include coded and non-coded information. Coded information originated by the host includes entry-separation marker signals. Individual marker signals are used at terminals to control access to associated particular time spaces of the multiplex frame. The host signals are serially stored by addressed terminals in the time sequence of transmission. The stored marker signals are protected from modification at terminals and control write-in access to storage spaced allocated to the associated time segments; thereby controlling terminal editing operations. Edited information in unprotected terminal storage spaces is easily segregated -- e.g., for compact transmission to the host -- by reference to the stored marker signals. When the non-coded signals comprise raster scanned picture information displayable at terminal display apparatus the markers are used to generate cursors indicating edit-accessible positions (e.g., character entry spaces). A distinct displaced cursor provides unique indication of the space next accessible for entry in a normal keying (i.e., typing) sequence.