Communications: electrical – Systems – Portable self-contained
Patent
1976-09-08
1978-08-22
Curtis, Marshall M.
Communications: electrical
Systems
Portable self-contained
178 30, G06F 314
Patent
active
041092449
ABSTRACT:
A CRT display system is connected to a central processing unit over a bus and includes a random access memory which is filled and modified under the control of the computer and contains a sequence of codes defining characters to be displayed on the screen in successive locations. An oscillator controlled divider chain increments an address counter and also provides vertical and horizontal synchronization and retrace signals. A character generator which receives a character code from a RAM location designated by the counter as well as timing signals from the divider chain controls intensity modulation of the CRT display. Multiplexers interposed at various points in the divider chain receive the output of several stages of the preceding divider and operate under control from the CPU to determine which output is provided to the next element in the chain, thereby controlling the character size and spacing on the screen. During the vertical retrace a signal is provided by the divider chain to the CPU and major changes are made in the contents of the RAM. When the CPU is changing the RAM contents during the display process, the character being provided by the CPU is provided to the character generator rather than the character at the RAM stage designated by the counter. This produces an instantaneously erroneous display but substantially simplifies the system's circuitry.
REFERENCES:
patent: 3559207 (1971-01-01), Atkinson
patent: 3637997 (1972-01-01), Petersen
patent: 3848232 (1974-11-01), Leibler et al.
patent: 3895374 (1975-07-01), Williams
Barnich Richard G.
Hakeem Timothy M.
Curtis Marshall M.
Process Computer Systems, Inc.
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