40 lines
1.6 KiB
Plaintext
40 lines
1.6 KiB
Plaintext
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)
|
|
|