Display control device

A display control device for accessing a memory to read out image data to be displayed on an image device in an image display scanning system in which an image display is formed of horizontal scanning lines with a preselected timing, comprising:

• scanning counter means incremented at a rate based on a required timing of access to said memory for generating a count which is repeated in accordance with the preselected timing of said image display scanning system;
• address generating means responsive to said scanning counter means for generating sequential addresses for accessing said memory;
• timing signal generator means responsive to said scanning counter means for generating a horizontal synchronizing signal and a vertical synchronizing signal based on said count, wherein said timing signal generator means includes means for discriminating between an odd-numbered display field and an even-numbered display field so that said timing signal generating means provides interlace scanning, wherein said scanning counter means includes a first counter driven by a clock signal having a frequency based on said required timing of access to said memory so as to produce an output to said timing signal generator means for generating said horizontal synchronizing signal, and a second counter driven by a signal corresponding to said horizontal synchronizing signal so as to produce an output to said timing signal generator means for generating said vertical synchronizing signal, and wherein said timing signal generator means further includes means for comparing the output of said first counter to a first preselected value and for resetting said first counter when a match is detected and means for comparing the output of said second counter to a second preselected value and for resetting said second counter when a match is detected;
• synchronizing signal generator means responsive to said timing signal generator means for generating as internal periodic synchronizing signal;
• control terminal means for transmitting or receiving said internal periodic synchronizing signal or an external periodic synchronizing signal respectively;
• switching means for connecting said control terminal means either to said synchronizing signal generator means for sending out said internal periodic synchronizing signal or to said scanning counter means and said discriminating means so that a periodic initialization of said scanning counter means is effected and said discriminating means is periodically set to a predetermined state in response to a received external periodic synchronizing signal;
• data storing means coupled to said timing signal generator means and to data terminals to be coupled to a data bus line for storing data, and including first register means for storing data representing said first preselected value and second register means for storing data representing said second preselected value;
• and
• address register means, coupled to said data storing means and to said data terminals, for storing selection data provided from said data terminals, and for indicating one of said first and second register means in accordance with the stored selection data such that predetermined data from said data bus line is stored in said register means indicated by said stored selection data.

A system including memory means for storing image data, a central processing unit coupled to said memory means and a display system coupled to said central processing unit and said memory means, wherein said central processing unit controls said display system and supplies image data to said memory means, and wherein said display system displays image data stored in said memory means on a display device as an image display formed of horizontal scanning lines with a preselected timing, said display system comprising:

• means including at least first and second display control devices for accessing said memory means to read out said image data, each of said first and second display control devices including
• (a) scanning counter means, incremented at a rate based on a required timing of access to said memory means, for generating a count which is repeated in accordance with the preselected timing of said display system,
• (b) address generating means responsive to said scanning counter means for generating sequential address for accessing said memory means,
• (c) timing signal generator means responsive to said scanning counter means for generating a horizontal synchronizing signal and a vertical synchronizing signal based on said count, wherein said timing signal generator means includes means for discriminating between an odd-numbered display field and an even-numbered display field so that said timing signal generating means provides interlace scanning, wherein said scanning counter means includes a first counter driven by a clock signal having a frequency based on said required timing of access to said memory means so as to produce an output to said timing signal generator means for generating said horizontal synchronizing signal, and a second counter, driven by a signal corresponding to said horizontal synchronizing signal so as to produce an output to said timing signal generator means, for generating said vertical synchronizing signal, and wherein said timing signal generator means further includes means for comparing the output of said first counter to a first preselected value and for resetting said first counter when a match is detected, and means for comparing the output of said second counter to a second preselected value and for resetting said second counter when a match is detected,
• (d) synchronizing signal generator means, responsive to said timing signal generator means, for generating an internal periodic synchronizing signal,
• (e) control terminal means for transmitting or receiving said internal periodic synchronizing signal or an external periodic synchronizing signal respectively,
• (f) switching means for connecting said control terminal means either to said synchronizing signal generator means for sending out said internal periodic synchronizing signal or to said scanning counter means and said discriminating means so that a periodic initialization of said scanning counter means is effected and said discriminating means is periodically set to a predetermined state in response to a received external periodic synchronizing signal,
• (g) data storing means coupled to said timing signal generator means and to data terminals to be coupled to said central processing unit for storing data, and including first register means for storing data representing said first preselected value and second register means for storing data representing said second preselected value,
• (h) address register means coupled to said data storing means and to said data terminals for storing selection data provided from said central processing unit, and for indicating one of said first and second register means in accordance with the stored selection data such that predetermined data from said central processing unit is stored in said register means indicated by said stored selection data;
• display means connected to said memory means for displaying image data read out of said memory means in response to said first and second display control devices, respectively, as superimposed images with identical timing;
• and
• synchronizing control means for connecting said control terminal means of said first display control device to said control terminal means of said second display control device, so that said periodic synchronizing signal generated in one of said first and second display control device may be applied to the other of said first and second display control devices.