> |< Diode > > \ Resistor > / > \ > / > > ================================================= > > +5v----------+--+--+--+ > | | | | > \ \ \ \ > / / / / > \ \ \ \ > / / / / > | | | | > D0---|<------O--O--O--O > | | | | > D1---|<------O--O--O--O (This bunch of "O"s is a matrix-type keypad > | | | | sort of thing.) > D2---|<------O--O--O--O > | | | | > D3---|<------O--O--O--O > | | | | > ERR----------+ | | | > | | | > SELIN-----------+ | | > | | > PE-----------------+ | > | > ACK-------------------+ > I'll have to double check, but I know that some parallel ports use an open collector archetecture for some of the data lines. It sort of limits the bidirectionality of the port, but it's cheaper to produce. (Again I'll and check for which lines and get back to you). While this occurs far less in more recent parallel port hardware, many older machines have this problem & many wearables are made from older machines. What this means is that without a pullup resistor in place, you will burn out the line trying to source enough current to bring it high. TTL circuit have pullup resistors built into them, so you can simply connect your ttl circuits up without the need for one, but some folks got cheap with the parallel port, (mostly, I imagine, because when it was originally created most folks felt it would only ever be used to hook up a printer with) Incidently a pullup resistor is simply a resistor connected like this... + 5 V | | \ / \ / | D1 ---------- (Your hardware here) Noah The sometimes correct.. ;-> -- Subcription/unsubscription/info requests: send e-mail with subject of "subscribe", "unsubscribe", or "info" toWear-Hard Mailing List Archive (searchable): http://wearables.ml.org
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