TrueTime VME-SG2 560-5608, Руководство пользователя

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Rev. F
Generator Mode - In this mode the VME-SG-GPS card operates as a simple
generator that increments time using the internal or external time base. Some
generator controls available are start and stop, external start via an external
pulse and time preset.
GPS SYNC-GEN - In this mode the VME-SG-GPS card will use the GPS Engine
to determine time and position. Most generator controls as described above are
disabled in the Sync-gen modes.
IRIG B SYNC-GEN - In this mode the VME-SG-GPS card will use an external
time code input as a time reference. The input code format is IRIG B (amplitude
modulated) or IRIG B (DC shift at RS-422 logic levels). The format is selected
using Configuration Register 2, bit 3. When IRIG B at RS-422 levels is used the
signal input is terminated with a 120 ohm resister when a jumper is installed on
JP1 pins 2 and 3.
b) Generator Start/Stop - The Generator accumulates time when bit 2 is
zero. The Generator stops when this bit is a 1.
c) Generator Preset - Bit 3 controls the presetting of the Generator time.
When this bit is set the VME-SG-GPS will clear the Generator time counters (unit
microseconds through hundreds of microseconds) and transfer the time found in
the Time Preset registers (milliseconds through thousands of years). This bit will
self clear after the preset has completed.
d) External Start Enable - Bit 4 enables the Generator External Start
function. This feature allows the user to synchronize the card in the generator
mode to an external reference 1PPS pulse.
After the generator mode is selected, connect the external start 1 PPS at either
the External Event BNC on the front panel or on pin C7 of the P2/J2 connector.
First, determine if the rising or falling edge of the reference 1 PPS marks the
beginning of the second and select the appropriate edge as described under
CONFIGURATION REGISTER 2, External Event Falling Edge Select in this
section.
Second, stop the Generator using bit 2 as described above under Generator
Start/Stop.
Next, load the start time into the Preset Time Registers as described later in this
section.
Finally, set bit 4 of Configuration Register 1. The next 1 PPS edge will Start the
generator. Set bit 4 in the second prior to the start time.
e) External Oscillator Select - Set bit 5 to select the external 10 MHz input
as the Generator time base. Clear bit 5 to select the internal time base. The
external oscillator input is on pin C8 of the P2/J2 connector. An external
oscillator should only be selected in the generator mode. The 10 MHz input
must be at TTL logic levels. The signal duty cycle should be greater than 10%.
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