Circuit for sensing whether or not an add-in board is inserted i

Details Circuit for sensing whether or not an add-in board is inserted i Circuit for sensing whether or not an add-in board is inserted i

1994-09-26

1997-03-18

Westin, Edward P.

Electronic digital logic circuitry

Interface

326 82, 235441, H03K 190175

Patent

active

056126344

ABSTRACT:
In an environment where a contact of a mother board is connected to a logic HIGH level voltage through a strong pull-up resistor, and a corresponding contact of an add-in board is connected to an open-drain driver, such that a control line driven by the open-drain driver is provided through the two contacts in normal mode operation when the two contacts make electrical connection, a circuit to sense whether or not the contact of the add-in board is making electrical connection with the contact of the mother board includes a weak pull-down resistor connected at one end to a node connecting the output of the open-drain driver to the contact of the add-in board, and connected at the other end to a ground reference. Accordingly, a voltage detected on the node is pulled up close to the logic HIGH level voltage if the contact of the add-in board is making electrical connection with the contact of the mother board and the open-drain driver is turned off, and is pulled down close to ground if the contact of the add-in board is not making electrical connection with the contact of the mother board and the open-drain driver is turned off. The voltage thus detected is provided to other circuitry on the add-in board, and/or back to a host computer on the mother board.

REFERENCES:
patent: 4675769 (1987-06-01), Marshall et al.
patent: 4885482 (1989-12-01), Sharp et al.
patent: 4948954 (1990-08-01), Dias
patent: 4990760 (1991-02-01), Tomari et al.
patent: 5162675 (1992-11-01), Olsen et al.
patent: 5266783 (1993-11-01), McAllister

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