National Instruments DAQCard-1200 - page 47

Chapter 3 Signal Connections

© National Instruments Corporation 3-25 DAQCard-1200 User Manual

Figure 3-15. Interval-Scanning Signal Timing

Use the final external control signal, EXTUPDATE*, to externally control

updating the output voltage of the 12-bit DACs and/or to generate an

externally timed interrupt. There are two update modes—immediate update

and delayed update. In immediate update mode the analog output is

updated as soon as a value is written to the DAC. If you select the delayed

update mode, a value is written to the DAC; however, the corresponding

DAC voltage is not updated until a low level on the EXTUPDATE* signal

is sensed. Furthermore, an interrupt is generated whenever a rising edge is

detected on the EXTUPDATE* bit. The interrupt service routine can write

the next value to the DAC. When the EXTUPDATE* signal goes low, the

DAC will subsequently be updated. Therefore, you can perform externally

timed interrupt-driven waveform generation on the DAQCard-1200.

Notice that the EXTUPDATE* signal is level sensitive; that is, if you

perform writes to the DAC when EXTUPDATE* is low, the DAC is

updated immediately. Also notice that when EXTUPDATE* is low, the

signal is susceptible to noise caused by switching of other lines. Because

the signal is TTL-compatible, the lower noise margin for logical 0 can

result in transitions to a logical 1 due to noise and thereby generate false

interrupts. Therefore, the width of EXTUPDATE* pulse should be as short

as possible and greater than 50 ns.

Figure3 -1 6 illustrates a waveform generation timing sequence using the

EXTUPDATE* signal and the delayed update mode. The DACs are

updated by a high level on the DAC OUTPUT UPDATE signal, which in

OUTB1

EXTCONV*

CONVERT

GATE

tw = 50 ns

td = 50 ns

ADC CH CH1 CH0 CH1 CH0

Contents

Main Page Important Information Warranty Copyright Trademarks WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS Contents Chapter 4 Theory of Operation Page Tables About This Manual Organization of This Manual Conventions Used in This Manual National Instruments Documentation Related Documentation Introduction About the DAQCard-1200 What You Need to Get Started Software Programming Choices LabVIEW and LabWindows/CVI Application Software NI-DAQ Driver Software Register-Level Programming Optional Equipment Unpacking Installation and Configuration Installation Configuration Analog Input Configuration Analog Input Polarity Analog Input Mode RSE Input (Eight Channels, Default Setting) NRSE Input (Eight Channels) DIFF Input (Four Channels) Analog Output Configuration Analog Output Polarity Digital I/O Configuration Counter Configuration Signal Connections I/O Connector Figure 3-1. DAQCard-1200 I/O Connector Pin Assignments Signal Connection Descriptions Analog Input Signal Connections + Types of Signal Sources Floating Signal Sources Ground-Referenced Signal Sources Input Configurations Differential Connection Considerations (DIFF Configuration) Differential Connections for Grounded Signal Sources Figure 3-3. Differential Input Connections for Grounded Signal Sources Differential Connections for Floating Signal Sources Figure 3-4. Differential Input Connections for Floating Sources Single-Ended Connection Considerations Single-Ended Connections for Floating Signal Sources (RSE Configuration) Single-Ended Connections for Grounded Signal Sources (NRSE Configuration) Common-Mode Signal Rejection Considerations Analog Output Signal Connections Digital I/O Signal Connections Page Port C Pin Connections Timing Specifications Mode 1 Input Timing Mode 1 Output Timing Mode 2 Bidirectional Timing Page DAQ and General-Purpose Timing Signal Connections DAQ Timing Connections Page Page Page General-Purpose Timing Signal Connections Page Page Figure 3-18. Frequency Measurement Application Chapter 3 Signal Connections DAQCard-1200 User Manual 3-30 National Instruments Corporation Figure 3-19. General-Purpose Timing Signals The GATE and OUT signals in Figure3-19 are referenced to the rising edge of the CLK signal. Power Connections National Instruments Corporation 4-1 DAQCard-1200 User Manual Theory of Operation This chapter explains the operation of each functional unit of the DAQCard-1200. Figure 4-1. DAQCard-1200 Block Diagram Functional Overview The block diagram in Figure 4-1 shows a functional overview of the DAQCard-1200. PC Card I/O Channel Interface Circuitry Timing Chapter 4 Theory of Operation Figure 4-3. Timing Circuitry DAQCard-1200 User Manual 4-4 National Instruments Corporation Analog Input Analog Input Circuitry Page Data Acquisition Timing Data Acquisition Operation Continuous Data Acquisition Interval Data Acquisition Data Acquisition Rates Page Analog Output Analog Output Circuitry Power-On State DAC Timing Digital I/O Calibration Calibration at Higher Gains Calibration Equipment Requirements Using the Calibration Function Page A Specifications Analog Input Input Characteristics Transfer Characteristics Amplifier Characteristics Dynamic Characteristics Stability Analog Output Output Characteristics Transfer Characteristics Page Timing I/O Digital Trigger Bus Interface Power Requirement Physical Page B Differences among the Lab-PC+, the DAQPad-1200, and the DAQCard-1200 Page C Power-Management Modes Page D PC Card Questions and Answers Configuration Operation Resources Page Page E Technical Support Resources NI Web Support Online Problem-Solving and Diagnostic Resources Software-Related Resources Worldwide Support Glossary Numbers/Symbols A B C D E F G Page Page V Index Numbers A B C D E F G I L M N O R S T U V W