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Signature Analysis Testing of Multiple Pages of a CRT Character Generator Using DMA Terminal Count

IP.com Disclosure Number: IPCOM000043862D
Original Publication Date: 1984-Oct-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Davis, GT: AUTHOR [+3]

Abstract

A technique is described whereby up to eight separate CRT character generator pages are tested in a single test operation. The block diagram, as shown in the figure, provides the ability to test multiple pages of a CRT character generator, all within a single display frame. The terminal count output from the direct memory access controller (DMA) 10 conditions flip-flop 11 in a latched position because the terminal count signal is a short pulse which cannot be recognized by an Intel 8085 microprocessor. The output of flip-flop 11 then provides an interrupt to the microprocessor 12.

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Signature Analysis Testing of Multiple Pages of a CRT Character Generator Using DMA Terminal Count

A technique is described whereby up to eight separate CRT character generator pages are tested in a single test operation. The block diagram, as shown in the figure, provides the ability to test multiple pages of a CRT character generator, all within a single display frame. The terminal count output from the direct memory access controller (DMA) 10 conditions flip-flop 11 in a latched position because the terminal count signal is a short pulse which cannot be recognized by an Intel 8085 microprocessor. The output of flip-flop 11 then provides an interrupt to the microprocessor 12. A memory write signal from the microprocessor 12 is used to reset the flip-flop 11 so that when the microprocessor 12 responds to the interrupt and starts to push the contents of the previous program counter onto the stack, the flip-flop 11 is reinitialized automatically so as to be ready for the next terminal count. The display size is programmed large enough to display the entire character set in all eight pages or character fonts by initializing the internal registers of the CRT controller 16. At the response to the interrupt, the microprocessor 12 first initializes the DMA controller 10 for the next few display lines, or the next page in the character generator. Then the character generator page is changed by writing to input/output (I/O) port 13 which controls the high- order address...