VXI SVM2608 user manual Acquiring Data, Triggering

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The counts stored in memory are 16 bits SIGNED integers. The most significant bit represents the SIGN. Thus, the hex number 0x4000 and the hex number of 0xC000 represent the same signal amplitude but in opposite directions, where 0x4000 represents a positive signal while 0xC000 is a negative signal with the same amplitude.

To translate a raw count value into a voltage, multiply the raw count value by the bit weight. The following example shows this conversion for a SVM2608 using the 10.0 V range:

A reading of 0x4000 = 16,384 counts

Voltage = Counts * Bit Weight

Voltage = 16384 counts* 305.176 µV/count

≈5.0 volts.

A reading of 0xC000 = -16,384 counts

Voltage = -16384 counts * 305.176 µV/count

≈-5.0 volts.

Similarly, for the 5 volt range:

A reading of 0x4000 = 16,384 counts

Voltage = 16,384 counts * 152.588 µV/count

≈2.5 volts.

Data acquisition can be made in two modes: Linear or FIFO. In FIFO mode, data can only be read from a fixed address (FIFO register), while in Linear mode, data can be read from any address in the memory space of a channel. Linear mode also offers a two more options for acquisition: Pre-Triggerand Delayed Trigger.

In FIFO mode, data can be retrieved while the acquisition is still in progress. However, if the memory is not read and the acquisition continues running, new incoming data will overwrite older data and the older data will be lost. It is also NOT possible to run a measurement command in FIFO mode.

Acquiring Data

To acquire data, a channel must first be Armed. When a channel is armed, it starts its local Sample Clock and waits for a Trigger Event to begin sampling. The channel must remain Armed for the entire duration of the acquisition process. Clearing the ARM bit will reset the internal state-machines and stop acquisition. Data capturing starts when a Trigger Event occurs. A trigger event can be caused by an external trigger source, the signal under test or forced by setting a bit in a register.

Triggering

An external signal, other than one of the sampled signals, can be used to trigger any or all of the channels. This external signal is compared to a threshold level set by a local DAC and a high- speed comparator is used to generate an External Trigger signal.

The signal under test can also be used to trigger an acquisition. The signal is compared to a threshold level set by a local DAC and a high-speed comparator is used to generate a Channel Trigger signal. Each channel has its own DAC and its own comparator, thus, each channel can generate a Trigger signal independent of the other channels. Acquisition on any channel can be triggered by any other Channel Trigger signal (Channel 0 can be triggered by Channel 0 Trigger, Channel 1 Trigger, Channel 2 Trigger, or Channel 3 Trigger) even if the other channels are not armed and are not acquiring any data. Only one channel can be the trigger source at any time and the trigger sources cannot be AND’ed or OR’ed together.

SVM2608 Introduction

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Contents SVM2608 VXI Technology, Inc Table of Contents Self Test Command Limitation of Warranty WarrantyCertification Restricted Rights LegendSteve Mauga, QA Manager EMCTerms and Symbols Service should only be performed by qualified personnelUse Proper Power Cord Use Proper Power SourceGround the Product Avoid Electric ShockOperating Conditions Improper UseVXI Technology Cleveland Instrument Division VXI Technology World HeadquartersVXI Technology Lake Stevens Instrument Division Technical SupportVXI Technology, Inc SVM2608 Preface Overview IntroductionScale Triggering Acquiring DataDelayed Trigger Linear ModePre-Trigger Commands Fifo ModeCalibrations Test BusOption SVM2608 Block Diagram Physical Description SVM2608 Environmental SpecificationsGND CH1I CH3I Front Panel Interface WiringGND CH1I+ GND CH3I+ Exttrigin CH0I CH2IMtbf SVM2608 SpecificationsOption 1 SVM2608-01 VXI Technology, Inc SVM2608 Introduction Setting the Chassis Backplane Jumpers Calculating System Power and Cooling RequirementsRotary Switch Locations Setting the Base AddressDivide Decimal ExampleMSB LSB Module INSTALLATION/REMOVAL Switch to C and the front switch toFunction Offset Device Memory MapsReserved Register OffsetMS = Most Significant LS = Least Significant SVM2608 A32 Register MAP0x72 Command Register Channel 0x74 Databyte Ordering Determining the Register Address Description of Registers Accessing the RegistersSysfailctl INTLVL2 Force Trigger, Start Register 0x02 Read & WriteHSTRIGSRC2 EXT Trig SlopeReserved TimeoutctlExternal Trigger Level 0x06 Read & Write 4WIREOHMS 2WIREOHMSLINEAR/FIFO ATTN-GAIN1-GAIN0Sample Rate 0x0E, 0x36, 0x5E, 0x86 Read & Write Sample Rate 0x0C, 0x34, 0x5C, 0x84 Read & WriteKHz Channels 0-3/5 MHz Channels 4-5 LPF Control This bit Sample Rate, High-Speed 0xAE, 0xD6 Read & Write Sample Rate, High-Speed 0xAC, 0xD4 Read & WriteTimeout 0x1C, 0x44, 0x6C, 0x94, 0xBC, 0xE4 Read & Write Fifo Data 0x26, 0x4E, 0x76, 0x9E, 0xC6, 0xEE Read Only Fifo Data 0x24, 0x4C, 0x74, 0x9C, 0xC4, 0xEC Read OnlyReserved Registers 0xF8 0xFC Trigger Delay = Measurement Commands Microprocessor CommandsCaptured Data Calculations Resistance Measurement Offset Method Self Test CommandResistance Measurement Dynamic Method Example Preset Setting Measurement CommandsSample Points Calibration CommandsSample Rate Trigger Event Forced TriggerPage Error Processing There are no errors in the queue Diagnostic Commands Changes become effective the next time the module powers up Examples Example 2 Setting Channel 2 to Acquire 200,000 SamplesExample 3 Setting Channel 2 to Pre-acquire 100,000 Samples Timeout Register = Timeout Base * 213 + Timeout Counter Timeout Counter = Timeout / Timeout Base ClockVXI Technology, Inc SVM2608 Programming Data Swapping Example Appendix aVXI Technology, Inc SVM2608 Appendix a Index
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