Many military VME-based applications require synchronization or time correlation. Meanwhile, thanks to the ongoing magic of semiconductor integration, newer technology and smaller components, today’s PMC cards are supporting the same functionality as the VME timing cards. That’s led to a rich crop of VME and PMC precision timing cards that provide accurate time-of-day data. These cards acquire time from a time source to which an onboard oscillator is disciplined. The oscillator frequency is then used to provide the boards’ sub-second time, as well as all of the boards’ time and frequency outputs. Using a 10 MHz oscillator, the VME and PMC cards provide zero latency 100 ns time resolution in the time registers.

Time is acquired from a variety of time sources, including the Global Positioning Satellite system (GPS) or time codes such as IRIG. The cards also have the ability to synchronize to an external 1 pps signal. The 1 pps signal does not carry any time data, so in this case the user may program the current time to the card. If the synchronization source is interrupted or absent, the disciplined oscillator will count time in a “flywheel state” until synchronization is achieved. If there is no synchronization source, the card will function in “Free Run Mode,” starting the time count from a programmed time.

VME and PMC board level products provide time to a host computer. The board time may be used to synchronize the PC clock or to synchronize multiple computers on a network to the same time base. The VME and PMC timing boards also function as time code generators, proving time code outputs to synchronize other cards or equipment. Typical applications include: range timing, data analysis systems, power utilities, control rooms, etc.

Free Run Mode

Once the VME or PMC timing card is supplied with a synchronization source, or set up to provide time in Free Run Mode, there are a variety of functions that these cards support, including an event capture function, an alarm output, as well as a frequency and/or pulse rate output. The frequency outputs will typically include a selectable 1, 5 and 10 MHz output, a dedicated 1 pps output and a programmable rate output. Each of these functions has an associated interrupt, allowing the user to integrate the desired functionally into their software application using interrupt driven algorithms.

The event capture function is a TTL card input that will latch a time associated with an external event. When the TTL level changes, the time is stored in a dedicated set of registers for retrieval later. In addition, the user may generate an interrupt to automate the time reads as they occur. This feature is used for data logging or correlation, or for time tagging any external event the user chooses. For example, there are many external events associated with a missile launch used to evaluate performance.

TLL Output and Interrupts

The alarm output is based on a TTL output signal that occurs at a pre-programmed time. When the board time matches the programmed time, the card generates an output TTL pulse and/or an associated interrupt. This feature may be used to start an external process or to activate outside equipment. In addition, the interrupt may be used to start a software-based process. Common applications include ATE control to start and/or stop various tests of military systems, event simulations to test event measurement systems and missile lift-off simulations.

There are a variety of frequency and pulse rate outputs supported. These typically include 1, 5 and 10 MHz frequency outputs, as well as programmable pulse rates. Again, these pulse rate outputs have an associated interrupt. Pulse rates and frequency outputs are typically used to synchronize external periodic events. For example, multiple passive radars may be synchronized, improving the cost of using dual active radars for weather tracking in aviation. Also, multiple cameras may be synchronized to track moving objects, logging data with time and GPS position, determining the exact location of the object.

Flexibility for System Integration

Board-level products like the VME and PMC cards offer the system integrator flexibility, by allowing the user to configure the card for unique applications, implementing only those features required for a specific application. In addition, using interrupt, the integrator may create an interrupt driven algorithm to write software specific to each unique application.