National Instruments 653 Series User Manual

Also see for 653 Series: User guide

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National Instruments 653 Series User Manual Manual pdf 57 page image

Chapter 3 Timing DiagramsNI 653X User Manual 3-2 ni.comFigure 3-1. Internal Request Timing DiagramExternal REQ Signal SourceUse an external request when you want to time data transfers using anexternal signal on the REQ pin of the I/O connector. You can select thepolarity of the REQ signal. If you choose active high (default), the NI 653Xlatches the data on the I/O pins on the rising edge of the REQ signal. If youchoose active low, the NI 653X latches the data on the I/O pins on the fallingedge of the REQ signal. The low time and high time of the REQ signal musteach be >20 ns. The minimum duration for a period of the REQ signal is50 ns.Parameter Descriptiont c* Cycle timetw* Width of pulsetp Propagation time to valid output datat su Setup timeth Hold time* The NI 6534 transfers data at 20 MHz when the cycle time (tc) for REQ pulse is 50 ns and width of the REQ pulse (tw)is 20–30 ns.dtp will remove barData Valid(Output Mode)Data Valid(Input Mode) tsu30 nsMinth0 nsMintp30 nsMaxtcProgrammable:t c = Interval x Timebase PeriodProgrammable:tw = One Timebase PeriodREQ if Active LowREQ if Active Hightw