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Display interface system using buffered VDRAMs and plural shift registers for data rate control between data source and display
| Details |
Inventors: McCord, Donald G.;
Assignee:
Primary Examiner: Williams, Jr.; Archie E.
Assistant Examiner: Andrews; Malcolm
Attorney, Agent or Firm: Fliesler, Dubb, Meyer & Lovejoy
A virtual cathode ray tube device is used in a video graphics system having a source of data and a visual display device. This virtual CRT device includes a plurality of buffers, a plurality of VDRAMs, each of said VDRAMs having an internal shift register, a plurality of external shift registers, first apparatus for transferring data from said source of data to said buffers, second apparatus for transferring data from said buffers to said VDRAMs, third apparatus for transferring data from each of said VDRAMs to its internal shift register, and a fourth apparatus for transferring data from said internal shift registers to said plurality of external shift registers at a first rate. A fifth apparatus transfers data from said plurality of external shift registers to said visual display device at a second rate, said second rate being greater than said first rate. |
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DETAILED DESCRIPTION The present invention elates to a method and apparatus for permitting computer graphics systems designed to work with cathode ray tube displays to greatly expand their range of pixel resolution and increase their rate of drawing without compromising their feature set in any way.
The invention comprises a method and means to simulate a cathode ray tube in all of its characteristics from the perspective of the graphics system except in minimum refresh frequency, a means to store and maintain the image created by the computer graphics system, and to output it to the final viewing device.
Objects of this invention are a method and apparatus comprising an inexpensive device which will allow computer graphics systems using standard components to support high resolution and high performance and provide complete software compatibility with designs using the same components which interface directly to a cathode ray tube display.
In accordance with the above objects, a plurality of video dynamic random access memories (VDRAMs), each having an internal shift register, a plurality of buffers, a plurality of external shift registers and associated control and addressing circuits are provided.
In operation, data is transferred from a video data source in the graphics system to the VDRAMs via the buffers.
Thereafter, the data is transferred from the VDRAMs to their internal shift registers and then to a CRT via the external shift registers.
The data is transferred from the external shift registers to the CRT at a rate equal to a multiple of the rate at which the data is transferred from the VDRAMs' internal shift registers to the external shift registers, e.
g.
4.
times.
.
By using the VDRAM's, buffers and internal and external shift registers in the manner described, writing to the CRT and either updating or refreshing the VDRAM's is performed simultaneously.
This effectively decouples the limitations of the CRT and the video data source from each other and allows for higher rate data transfers to the CRT permitting the use of greater resolution CRTs with no loss in performance due to a lower rate of data transfer from the video data source
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I/O Systems 
