Chapter 3 Analog Output Timing/ControlDAQ-STC Technical Reference Manual3-12 ©National Instruments CorporationFigure 3-9. Internal UPDATE Timing3.4.4.2 External UPDATEIn the external UPDATE mode, externally generated UPDATE pulses enter the DAQ-STCthrough one of the PFI<0..9> or RTSI_TRIGGER<0..6> inputs or general-purpose counter 1.Alternately, the UPDATE may come from general-purpose counter 1. Only one timingparameter is available in this model—the delay between UPDATE pulses. This delay isdetermined by the period of the external UPDATE signal. The delay from START1 to the firstUPDATE depends upon the relationship between the START1 trigger and the externalUPDATE, and can vary. Figure 3-10 shows a sequence of externally timed UPDATE pulsesand indicates the delay from START1 to the first UPDATE.Figure 3-10. External UPDATE Timing3.4.5 Buffer Timing and Control for Primary Analog OutputSequences of UPDATE pulses are organized into buffers. A buffer consists of a fixed numberof data points that are output at a constant rate. The DAQ-STC can easily provide timing formultiple iterations of a single buffer (MISB). When a sequence of buffers is outputconsecutively, a waveform is generated. A waveform may consist of one MISB or it mayconsist of multiple MISBs. The DAQ-STC provides direct hardware support for the output ofa single MISB, output of one MISB followed immediately by a second MISB, and output oftwo MISBs which alternate. The DAQ-STC can generate even more complex waveformsSTART1UPDATE (UI_TC)A B B BTiming ParameterSTART1UPDATEExternal UPDATE
