System for dual buffering of asynchronous input to dual port memory for a raster scanned display

A system for controlling the reading from and writing to dual-port memory for storing digital video data to be displayed on a raster scanned video display device, the video data being written to a write address in said memory and being read from a read address in said memory, wherein the video data is received asynchronously with respect to the video frame display rate, the system comprising:

• a first flip-flop having an input connected to a write sync signal source;
• a second flip-flop;
• two banks of dual-port memory, wherein a first output and a second output from said first flip-flop are connected to a write port enable input on a first one and a second one of said banks, respectively, and wherein a first output and a second output of said second flip-flop are connected to a read port enable input on a first one and a second one of said banks, respectively;
• address compare logic having an input connected to a read sync signal source and to read address and write address lines on each of said banks, and having an output connected to a clock input of said second flip-flop, said output being an alternate buffer output signal generated in response to a simultaneous presence of said read sync signal and a predetermined separation between said read address and said write address;
• wherein said display device is connected to a data output port of each of said banks;
• wherein each occurrence of said write sync signal causes said first flip-flop to toggle an output signal between said write port enable input on said first one of said banks and said write port enable input on said second one of said banks, and
• wherein said alternate buffer signal causes said first flip-flop to toggle an output signal between said read port enable input on said first one of said banks and said read port enable input on said second one of said banks.

A system for controlling the reading from and writing to dual-port memory for storing digital video data to be displayed on an LCD display, the video data being written to a write address in said memory and being read from a read address in said memory, wherein the video data is received asynchronously with respect to the LCD frame display rate, the system comprising:

• two dual-port memory banks, each having a write port enable input and a read port enable input;
• read sync indication means, responsive to a simultaneous presence of said read sync signal and a predetermined separation between said read address and said write address, for generating an alternate buffer signal indicating that said write address and said read address are separated by a predetermined distance;
• first flip-flop means, responsive to a write sync signal, for toggling an output signal between said write port enable input on said first one of said banks and said write port enable input on said second one of said banks;
• second flip-flop means, responsive to said alternate buffer signal, for toggling an output signal between said read port enable input on said first one of said banks and said read port enable input on said second one of said banks.