Browse Prior Art Database

Frame Generation by CRT Controller

IP.com Disclosure Number: IPCOM000043033D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Iida, H: AUTHOR

Abstract

This article describes a technique of generating a frame pattern which defines the boundary of a variable screen area in a fixed screen. A CRTC (CRT controller) includes registers for defining the position and size of the variable screen area and, in response to the values in the registers, generates addresses for accessing a frame pattern generator to generate a corresponding elemental graphic pattern for each of frame portions in synchronism with scanning. In Fig. 1 illustrating a raster scan CRT display screen format, fixed full screen A is for graphic information display and screen B is for character information display, for example. The screen area B may be selectively inserted into the screen A with variable position and size. The frame is displayed in the form of a rectangular pattern surrounding the screen area B.

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Frame Generation by CRT Controller

This article describes a technique of generating a frame pattern which defines the boundary of a variable screen area in a fixed screen. A CRTC (CRT controller) includes registers for defining the position and size of the variable screen area and, in response to the values in the registers, generates addresses for accessing a frame pattern generator to generate a corresponding elemental graphic pattern for each of frame portions in synchronism with scanning. In Fig. 1 illustrating a raster scan CRT display screen format, fixed full screen A is for graphic information display and screen B is for character information display, for example. The screen area B may be selectively inserted into the screen A with variable position and size. The frame is displayed in the form of a rectangular pattern surrounding the screen area B. To generate the frame pattern, only eight elemental graphic patterns a-h are required, as shown in Fig. 2. Each of the frame portions a-h is generated by a corresponding one of the graphic patterns a-h. In addition to conventional registers 22 (Fig. 3) for setting full screen A parameters such as horizontal width (HWA) and vertical width (VWA), CRTC 10 further includes registers 14, 16, 18 and 20 for defining the position and size of the variable screen area B. Registers 14, 16, 18 and 20, respectively, store horizontal and vertical coordinates of the start point of the screen B(HSB and VSB), horizontal width of the screen B(HWB) and vertical width of the screen B(VWB). The CRTC 10 includes control register 12 having a set frame bit which is set ON by so...