f89ba@rigel.efd.lth.se (04/09/91)
I'm planning on letting my modem (COM3) and the LPT2 port share IRQ5. This should work since I don't use the second parallel port but need an extra serial port. However, is it possible to let two devices (in particular a serial port and a parallel port) share an interrupt line without the risk of damaging the computer's hardware? Although not particularly well informed in this area, I could imagine a scenario with one device raising the signal and the other one lowering it, causing a "short circuit" between +5 volts and 0 volts, or am I way off here? In either case, I would appreciate some facts before I flip the dipswitch! Please email any responses since I cannot keep up with comp.sys.ibm.pc.misc Bengt Ask, Lund Institute of Technology, Lund, Sweden
ntaib@silver.ucs.indiana.edu (Nur Iskandar Taib) (04/11/91)
>However, is it possible to let two devices (in particular >a serial port and a parallel port) share an interrupt >line without the risk of damaging the computer's hardware? >Although not particularly well informed in this area, I could >imagine a scenario with one device raising the signal and >the other one lowering it, causing a "short circuit" between >+5 volts and 0 volts, or am I way off here? I always thought the computer's bus uses assertion- level logic, i.e. if one device causes a line to go high, the line will go high no matter what the other devices on that line are doing. The equivalent of a logical multi input OR. Assertion level logic devices require a terminator resistor between the line and ground. -- ------------------------------------------------------------------------------- Iskandar Taib | The only thing worse than Peach ala Internet: NTAIB@AQUA.UCS.INDIANA.EDU | Frog is Frog ala Peach Bitnet: NTAIB@IUBACS ! -------------------------------------------------------------------------------