Control device for writing for multi-window display

Claim 1

In a control device for writing for a multi-window display system including display controlling means and a display frame memory, wherein, in a write cycle, data is written into said display frame memory according to an address signal supplied from said display controller means, and, in a display cycle, the data which is stored at the address specified by the address signal supplied from said display controller means is output, said control device further comprising: a write controlling mapping buffer for storing regional data about window display regions at corresponding addresses for the data to be written into said display frame memory and for outputting a corresponding window identifying number when said display controlling means outputs an address during a write cycle; a window identification number register with a window identification number set therein corresponding to the data to be written into said display frame memory; and a coincidence detection circuit receiving the window identifying number from said write controlling mapping buffer corresponding to the address for the data to be written thereat and receiving the window identification number from said window identification number register for supplying, only when a coincidence between these two input window identification numbers is detected, said display frame memory with a signal allowing the data to be written in said frame memory.