40 lines
1.6 KiB
Plaintext
40 lines
1.6 KiB
Plaintext
AST RESEARCH TECHNICAL BULLETIN TB-0010 4-13-84
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IRQ-7 PARALLEL PORT CONTENTION
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IRQ-7 USED BY AST MULTIFUNCTION BOARDS
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FOR PARALLEL I/O PORT OPERATIONS
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In some of the earlier multifunction boards, where the parallel
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port is an option and that option is not included on the board, a
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problem is created.
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When this option, parallel port, was not ordered, a IC (74LS174)
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that governs the status lines for the parallel port was deleted
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on the bill of materials. Unfortunately, this IC also controls
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the IRQ-7 line. With this IC (74LS174) not present, it creates a
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low condition, via 74LS125, which causes contention with other
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devices trying to use IRQ-7. Example of circuit is attached.
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The IC (74LS174) must be installed for proper operation. Refer
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to schematics, at rear of user's manual, for correct location of
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74LS174 IC.
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AST Research suggests when working with dual in line packages,
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that you carefully place IC's in socket so that the legs insert
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properly into socket. Examine carefully after insertion and
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verify that all legs of IC are seated properly in their
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respective socket.
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NOTE: As a portion of the data is in pictorial form, it is not
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included here. To obtain a complete copy of this technical
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bulletin, contact:
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AST RESEARCH, INC.
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2121 Alton Avenue
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Irvine, California 92714
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ATTENTION: Product Support
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(Technical Bulletin)
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