National Instruments 700 User Manual
Also see for DAQCard-700: User manual
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Contents
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Signal Connections Chapter 3DAQCard-700 User Manual 3-14 © National Instruments CorporationTiming ConnectionsPins 38 through 48 of the I/O connector are connections for timing I/O signals. TheDAQCard-700 timing I/O uses an MSM82C54 counter/timer integrated circuit. All threecounters of the MSM82C54 are available at the I/O connector. One of these counters, counter 0,is used for data acquisition timing. Pin 40 carries an external signal, EXTCONV*, that can beused for data acquisition timing in place of counter 0 of the MSM82C54. This signal isexplained under Data Acquisition Timing Connections. Pins 38 and 41 through 48 carry general-purpose timing signals from the MSM82C54. These signals are explained under General-Purpose Counter and Timing Signal Connections later in this chapter.Data Acquisition Counter and Timing ConnectionsCounter 0 on the MSM82C54 counter/timer is used as a sample-interval counter in timed A/Dconversions. In addition to counter 0, you can use pin 40, EXTCONV*, to externally timeconversions. If you need to program this chip directly, refer to the optional DAQCard-700Register-Level Programmer Manual for the programming sequence needed to enable this input.Figure 3-7 shows the timing requirements for the EXTCONV* input. An A/D conversion isinitiated by a rising edge on the EXTCONV*. The data from this conversion is latched into theFIFO memory within 10 μs. The EXTCONV* input is a TTL-compatible signal.tw 200 ns MinimumA/D Conversion Starts HereV ILVIHtwEXTCONV*tint tint 10 μs Minimum(A/D interval)Figure 3-7. EXTCONV* Signal TimingNotice that EXTCONV* can only cause conversions to occur; you cannot use it as a monitor todetect conversions caused by the onboard sample-interval timer.General-Purpose Counter and Timing Signal ConnectionsThe general-purpose timing signals include the GATE, CLK, and OUT signals for the threeMSM82C54 counters, except CLK of counter 0 is not available on the I/O connector. You canuse the MSM82C54 counter/timers for general-purpose applications such as pulse and squarewave generation; event counting; and pulse-width, time-lapse, and frequency measurement. Forthese applications, CLK and GATE signals are sent to the counters, and the counters are |
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