US 5,293,587 A · Terminal control circuitry with display list processor that fetches instructions from a program memory, character codes from a display memory, and character segment bitmaps from a font memory

Abstract

Display control logic for a terminal controller with support for such features as windows and interlace. A display list processor (DLP) (20) communicates with a program memory (12) containing DLP instructions, a display memory (12) containing character codes and attributes for the display, and a font memory (13). As the DLP program executes, it causes accesses to the display memory and brings in character codes and attributes for ultimate display on the screen. These character codes and attributes, as well as information representative of the scan line are input to a video data queue (95). The queue entries are clocked out of the queue by a character clock (170) and are used to generate addresses to font memory. Bitmaps from font memory are read into a dot shifter (190). The DLP instruction set includes a DISPLAY STRING instruction which allows a portion of a scan line to be built up by specifying the length of the scan line segment and the starting address in memory. Thus, a scan line can be built up based on characters stored in different parts of memory. The instruction set also includes SET ROW, LOOP, and LOOPBACK instructions to specify a given row and to set up a loop so that all the scan lines in a given row of characters can be built up by repeated executions of the DISPLAY STRING instructions. It is also possible, to display the scan lines in any random scan line order.

Claims25

Dependent claims

For use in combination with a video display, a program memory for storing instructions, a display memory for storing display data items, and a font memory for storing font data, terminal control circuitry comprising:

means for fetching instructions from the program memory;
means, responsive to a predetermined type of instruction fetched from the program memory wherein the predetermined type of instruction specifies a starting address in the display memory and a character string length, for (1) retrieving a display data item from each of a number of contiguous storage locations in the display memory, starting at the specified starting address, said number being the specified string length, and (2) retrieving font data from the font memory for each display data item retrieved from the display memory, to generate a pixel pattern for a character segment of a scan line;
and
means, responsive to an additional predetermined type of instruction fetched from the program memory wherein the additional predetermined type of instruction specifies a number of blanks, for converting each specified blank to a blank segment of a scan line.

1 more element

video data queue means, having a queue input and a queue output, for storing entries communicated to said queue input and presenting stored entries at said queue output in FIFO fashion;
character output means, coupled to the font memory and responsive to entries at said queue output, for placing a character segment of a scan line on the display for each entry at said queue output;
and
control means, responsive to instructions fetched from the program memory, for directing operations in accordance with the instructions fetched;
said control means including means, responsive to a predetermined type of instruction, designated a DISPLAY STRING instruction, fetched form the program memory wherein said DISPLAY STRING instruction specifies a starting address and a character string length, for (1) retrieving a display data item from each of a number of contiguous storage locations in the display memory, starting at the specified starting address, said number being the specified string length, and (2) communicating each display data item, so retrieved, to said queue input as at least a portion of an entry.

2 more elements

scan line means for storing a range of scan lines and a current scan line;
string length mans for storing a string length and a current position in a string;
display memory address means for storing a starting display memory address and a current display memory address;
display memory access means, responsive to said current display memory address, for retrieving display data stored in said display memory at said current display memory address and for generating a signal signifying a successful memory access;
video data queue means, having a queue input and a queue output, for storing entries communicated to said queue input and presenting stored entries at said queue output in FIFO fashion;
means, responsive to said current scan line and said display data, for formulating entries and communicating said entries to said queue input, each of said entries including at least a portion that represents a font memory location;
font memory access means, responsive to a given entry at said queue output, for retrieving font data stored at a font memory location represented by said given entry;
video conversion means, responsive to said font data, for generating signals operative to place said font data on the display;
an instruction register;
means for fetching instructions from the program memory and loading said instructions in said instruction register;
and
control means, responsive to the content of said instruction register, for directing operations in accordance with the instructions fetched;
said control means including means, responsive to a predetermined type of instruction in said instruction register, designated a DISPLAY STRING instruction that specifies a string length and a starting address in the display memory, for (1) storing the specified string length and starting address in said string length means and said display memory address means, respectively, (2) activating said display memory access means a number of times corresponding to the specified string length to retrieve display data form a range of sequential locations starting at the specified starting address, and (3) activating said means for formulating entries;
and
said control means further including means, responsive to two predetermined instructions in said instruction register, designated LOOP and LOOPBACK instructions, said LOOP instruction specifying a series of scan lines, said LOOPBACK instruction specifying a transfer address, for (1) executing a sequence of instructions following the occurrence of said LOOP instruction until said LOOPBACK instruction is encountered by said control means, and (2) branching to the instruction immediately following said LOOP instruction until said sequence of instructions has been executed for all scan lines in the series specified by said LOOP instruction.

12 more elements

video data queue means, having a queue input and a queue output, for storing entries communicated to said queue input and presenting stored entries at said queue output in FIFO fashion;
character output means, responsive to entries at said queue output, for placing corresponding portions of characters on the display;
and
control means, responsive to instructions fetched from the program memory, for directing operations in accordance with the instructions fetched;
said control means including means, responsive to a predetermined type of instruction, designated a video instruction, fetched from the program memory wherein said video instruction specifies a number of display items, for (1) generating the specified number of display data items, (2) communicating each display data item, so generated, to said queue input as at least a portion of a queue entry.

2 more elements

Dependencies are inferred from the claim text.

Terminal control circuitry with display list processor that fetches instructions from a program memory, character codes from a display memory, and character segment bitmaps from a font memory

Life of this patent

Terminal control circuitry with display list processor that fetches instructions from a program memory, character codes from a display memory, and character segment bitmaps from a font memory

Life of this patent

Abstract

Claims25