External attribute logic for use in a word processing system

Claim 1

A circuit for controlling attributes of a plurality of characters on a display, comprising: (a) a processor for controlling the transfer of data associated with characters to be displayed, said associated data consisting of first data including elements defining said characters ordered in accordance with the positions of said characters on said display and second data in one-to-one correspondence with said first data, each element of said second data defining predetermined attributes for its associated character; (b) a memory operatively connected to said processor for storing said data; (c) communications means responsive to said processor and operatively connected to said memory for transferring said data from said memory; (d) display control means, responsive to said processor and operatively connected to said communications means for controlling the display of characters on said display in one-to-one correspondence with the elements of said first data, and for controlling the attributes of said characters in accordance with attribute input signals, said display control means including a first pair of line buffer registers for storing elements of said first data to be displayed as respective alternate lines of characters in correspondence to said elements of said first data; (e) external attribute control means operatively connected to said communications means and to said display control means for providing said attribute input signals, said external attribute control means including a second pair of buffer registers for storing elements of said second data, each member of said second pair of buffers corresponding to a member of said first pair; (f) synchronizing means for alternately reading members of said first pair of buffers synchronously with corresponding members of said second pair of buffers to define alternate lines of said characters and corresponding attributes to be displayed; and, (g) said processor controlling said display control means, said external attribute control means and said synchronizing means to alternately and synchronously output one of said first buffers and the corresponding one of said second buffers to define a line of said characters and corresponding attributes to be displayed in accordance with the elements of said first data and of said second data stored in said first and second buffers being output, and, substantially simultaneously, inputting other elements of said first and second data into the other members of said first and second pairs of buffers to define the next succeeding line of characters and corresponding attributes to be displayed.