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Flexible Character Generator Test

IP.com Disclosure Number: IPCOM000059988D
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 66K

Publishing Venue

IBM

Related People

Olson, DR: AUTHOR

Abstract

Terminals or other devices which use character generators can change the character generators at any time without the need to change the microcode for testing the generators. The first step in this design is to have three locations in the generators assigned to diagnostics. For instance, these locations could be x'c8', x'c9', and x'ca'. Next, the characters which are in locations x'55', x'5a', and x'a5' are duplicated in the diagnostic locations. These locations are not randomly selected but are chosen because they allow the address lines to be fully tested, as can be seen by observing the addresses in their binary form: b'01010101', b'01011010', and b'10100101'. This is the only constraint that is put on the design of the character generators. The next step is the design of the test itself.

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Flexible Character Generator Test

Terminals or other devices which use character generators can change the character generators at any time without the need to change the microcode for testing the generators. The first step in this design is to have three locations in the generators assigned to diagnostics. For instance, these locations could be x'c8', x'c9', and x'ca'. Next, the characters which are in locations x'55', x'5a', and x'a5' are duplicated in the diagnostic locations. These locations are not randomly selected but are chosen because they allow the address lines to be fully tested, as can be seen by observing the addresses in their binary form: b'01010101', b'01011010', and b'10100101'. This is the only constraint that is put on the design of the character generators. The next step is the design of the test itself. The test uses the same idea as the original type of test but it has a new twist. The new test starts by filling the screen with the three characters x'55', x'5a', and x'a5'. The dots are then counted as before, but then the count value is stored in memory. Next, the screen is filled with the three diagnostic characters x'c8', x'c9', and x'ca', and the dots are again counted. The two count values are now compared. If they are not the same, then the test indicates a character-generator problem. The last step in this design is to test against the case where the generator holds all ones or all zeros. To test against both cases, the screen is fill...