VXI Programmable Clock Generator Module

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The V660 is a single-width, C-size, register-based, VXIbus module providing a very flexible, programmable, multi-step clock generator for clocking ADCs and other front-end data acquisition modules.

The V660 provides a programmable sequence of clock rates for applications requiring different sampling rates during different phases of data collection. In addition, the V660 provides the ability to synchronize data sampling with external triggers as well as the ability to use an external clock source for output clock generation.

VXI Programmable Clock Generator Module: V660

V660 Data Sheet

Supporting Software

Supporting Chassis

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The V660 provides storage for sequences as long as 256 steps in which the frequency and duration of each step can be programmed. The V660 derives the output clock from one of three sources: a 10 MHz crystal clock, a 10.24 MHz crystal clock, or an external clock. Each step is defined by a division factor by which the base clock is divided. The duration of each step is determined by an associated count or external trigger. In the case of external trigger, the next step is initiated synchronously with the second tick of the base clock. An optional interrupt can be generated at the end of any step to signal the host processor that a new step has been initiated. The current frequency division, current step, sample count, previous step sample count, and program step address are directly accessible registers.

The frequency steps are loaded by software into the Program RAM. Each step includes a base frequency divisor, a step termination selection based on a specific count, external trigger, or software command only as well as a flag word that selects various options on a step-by-step basis. The frequency divisor is a 16-bit, modulo-N value by which the base frequency is divided. This provides a frequency range from 152.59 Hz to 10 MHz for the 10 MHz base clock. For low frequency applications, the base clock may be pre-divided by 256, providing frequency ranges of 0.5961 Hz to 39.062 kHz (10 MHz base clock) or 0.6104 Hz to 40.0 kHz (10.24 MHz base clock). A 24-bit count field permits up to 16 Msamples per step. When external trigger is selected, these bits are used to select a trigger divisor. A value of "4" would, for example, terminate the step on the 4th trigger.

The V660 is also capable of generating the following signals at the completion of a step:

  • Generate an interrupt
  • Generate a 35 ns, high-true, TTL output pulse on one or two front-panel Step Complete Strobes
  • Generate a 35 ns, high-true, TTL output pulse at the completion of the last program step

Additionally, the V660 can selectively set or clear a TTL-level signal at the start of each step. This signal is available on the Gate Out LEMO connector on the front panel.

The following control options are associated with each program step:

  • Select External Trigger, output pulse count, or software step termination
  • Disable clock output pulse for step duration (used to generate a delay)

The base clock frequency is selected by bits in a register in Operational Space.

A Previous Pulse Count register is provided. It is loaded with the current sample count at the end of each step and is accessible by VXI command. This register may be read following the completion of a step to determine the number of samples from that previous step. Thus, the actual number of samples acquired during a step that was terminated by an external trigger or VXI command can be determined.

The V660 supports both static and dynamic configuration. It may be accessed using A24/A16, D16 data transfers.

VXI Module Features

  • Creates Custom Clock Rate Profiles for Digitizing Signals
  • Programmable Frequency Sequence of up to 256 Steps
  • Programmable Frequency Range from 0.5961 Hz to 10.24 MHz
  • Strobe and Gate Outputs to Delineate Groups of Output Clocks
    (Steps) Programmably by Number of Clocks per Group,
    Number of External Input Triggers, or by VXI Command
  • Optional Interrupt Generation at End of Each Program Step

VXI Module Ordering Information

V660 Products and Part Numbers
Programmable Clock Generator V660-ZA11