Interface device for encoding a digital image for a CRT display

• US 4,121,283 A
• Filed: 01/17/1977
• Issued: 10/17/1978
• Est. Priority Date: 01/17/1977
• Status: Expired due to Term

• Current Assignee: Cromemco, Inc.
• Original Assignee: Cromemco, Inc.
• Inventors: Walker, James Terrell
• Primary Examiner(s): Chapnick, Melvin B.
• Application Number:
  US05/760,106
• Time in Patent Office: 638 Days
• Field of Search: 364/200 MS File, 364/900 MS File, 340/324 AD, 340/146.3 MA, 340/146.3 H, 235/151, 358/280, 358/260, 358/261
• US Class Current: 715/806
• CPC Class Codes: G09G 1/285 Interfacing with colour displays, e.g. TV receiver
• CPC Class Codes: G09G 5/391 Resolution modifying circuits, e.g. variable screen formats

Abstract

A display interface connected between a computer and a CRT device processes predetermined blocks of display data from predetermined locations in a memory of the computer to form pixels having predetermined characteristics in the display fields of the CRT device. A CRT display format of parameters such as color, pixel shape and size, and field shape and size, is controlled by input FORMAT DATA. The display resolution can be varied to accommodate the amount of data to be displayed within the desired field dimensions. The display data is retrieved from memory in data blocks, each of which is identified by a BLOCK ADDRESS. A single data block may occupy the entire display field; or may be displayed in a subfield simultaneously with other data blocks, or portions of data blocks, in the remaining subfields. The FORMAT DATA determines the subfield number and arrangement.

Claims

1. An interface device for connection between a computer and a CRT device for processing predetermined blocks of display data from predetermined locations in a memory in the computer to form pixels having predetermined characteristics in the display fields of the CRT device, the interface device comprising:

means for storing format data which defines the dimensions and number of fields displayed, and the characteristics of the pixels displayed therewithin;

control means responsive to the format when read out from the means for storing for coordinating the data processing cycle of the computer memory and the data display cycle of the CRT device;

pixel controller responsive to the read out format data for controlling the pixel characteristics and responsive to the control means for processing the display data;

video means for converting the processed display data from the pixel controller into analog signals and adapted to apply the analog signals to the video circuit of the CRT device; and

memory address means for addressing blocks of display data corresponding to the display fields of the CRT device, having a first address counter responsive to the format data for incrementing the least significant bit (LSB) portion of the memory address to the computer memory which defines the first dimension of each field displayed on the CRT device, and a second address counter responsive to the format data for incrementing the next LSB portion of the memory address to the computer memory which defines the second dimension of each field displayed on the CRT device.

2. The interface device of claim 1, wherein the memory address means has a block addresser responsive to the format data for providing the most significant bit portion of each memory address to the computer which addresses the block of display data corresponding to the field to be displayed on the CRT device.

3. The interface device of claim 2, wherein the format data determines the dimensions of the displayed pixel from a series of pixel dimensions.

4. The interface device of claim 3, wherein the fundamental pixel dimension is at least one CRT scan line in height and at least one clock period in width, and the dimensions of the other pixels in the series are multiples of the fundamental height and width dimension.

5. The interface device of claim 4, wherein the pixel controller extends the width dimension of each displayed pixel by increasing the number of clock periods during which the display data for each pixel is applied to the video means.

6. The interface device of claim 5, wherein the pixel controller has a clock responsive latch means for temporarily holding the display data for each pixel while applying the display data for each pixel to the video means.

7. The interface device of claim 4, wherein the pixel controller extends the height dimensional of each displayed pixel by redisplaying the same line of display data consecutively a predetermined number of times.

8. The interface device of claim 7, wherein the pixel controller has a line memory which temporarily stores each new line of display data for recycling the display data through the pixel controller to extend the height dimension of the pixels.

9. The interface device of claim 2, wherein the second address counter is responsive to the most significant bit of the first address counter to perform its incrementing

10. The interface device of claim 2, wherein the first address counter increments to address along a row of memory addresses containing display data which is sequentially displayed along at least a portion of a scan line of the CRT device.

11. The interface device of claim 10, wherein the first address counter addresses the display data for an entire scan line of the CRT device.

12. The interface device of claim 2, wherein the block addresser includes an incrementing means responsive to the format data for altering the most significant bit portion of the memory address.

13. The interface device of claim 12, wherein the incrementing means is responsive to the second address counter for changing the address of the most significant bit portion to identify other memory blocks.

14. The interface device of claim 13, wherein

the second address counter identifies the rows within each memory block;

each memory block provides the display data for one field of the display of the CRT device; and

the incrementing means is responsive to the most significant bit of the second address counter for identifying successive basic memory blocks each containing a field of display data for sequential display on the CRT device.

15. The interface device of claim 13, wherein the incrementing means is responsive to both the first and second address counter for systematically addressing multiple memory blocks causing at least a portion of the display data in each of the addressed memory blocks to be displayed simultaneously on the CRT device forming multiple subfields within the display field of the CRT device.

16. The interface device of claim 13, wherein the incrementing means is responsive to the most significant bits in both the first and second address counter for systematically addressing multiple memory blocks causing the display data in the addressed memory blocks to be displayed simultaneously on the CRT device forming a grid pattern of square subfields within the display field on the CRT device.

17. The interface device of claim 16, wherein the incrementing means identifies four basic memory blocks for simultaneous display in a quadrant pattern.

18. The interface device of claim 13, wherein the fundamental pixel height dimension is equal to the fundamental pixel width dimension forming a fundamental pixel which is square.

19. The interface device of claim 18, wherein the series of pixels are squares of increasing dimension.

20. The interface device of claim 19, wherein the series of square pixels increase in dimension by powers of two.

21. The interface device of claim 3, wherein the control means is horizontally and vertically synced with the CRT device.

22. The interface device of claim 21, wherein the control means provides horizontal and vertical sync signals to the CRT device.

23. The interface device of claim 22, wherein the control means includes an oscillator for establishing an internal clock which periodically generates sync signals to the CRT device and data request signals to the computer.

24. The interface device of claim 2, wherein the memory address means additionally provides memory addresses to the computer memory for identifying at least a portion of the format data in predetermined blocks at predetermined locations in the computer memory.

25. The interface device of claim 24, wherein the memory address means provides a display data address and a format data address for each pixel of the CRT display.

26. The interface device of claim 25, wherein the first and second address counters of the memory address means identify display data for each pixel within a display data memory block and also identifies corresponding format data for each pixel within a corresponding format data memory block.

27. The interface device of claim 26, wherein the block addresser of the memory address means provides twin addresses offset by a constant amount for identifying a display data memory block and a corresponding format data memory block.

28. The interface device of claim 2, wherein the format data includes intensity levels and the video means includes D/A logic responsive to the intensity levels for providing analog signals of corresponding amplitude levels.

29. The interface device of claim 28, wherein format data includes color data, and the video means includes delay means between the D/A logic and the CRT device for phase shifting the analog signal from the D/A logic causing a color display on the CRT device.

30. The interface device of claim 29, wherein the color data includes blue, red, and green, and the delay means shifts the phase of at least the red and green.

31. The interface device of claim 30, wherein the format data includes a plurality of intensity levels of blue, red, and green, and the D/A logic includes a blue decoder, a red decoder, and a green decoder for providing analog signals of corresponding output levels of blue, red, and green, respectively.