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