PCI_PCIe User Guide_RevA.pdf - Symmetricom

1.3. Functional Description
Code and GPS Mode, this major time is readily available, but in the Free Running and External 1 PPS
Modes, major time is not available and must be set manually by the user. The Timing Mode is
selected via the dual-port RAM interface as described in "Command 0x10: Set TFP Timing Mode" on
page 41, using command 10.
Mode 0 (Time Code Mode)
In Time Code Mode, the TFP derives time from the currently selected input time code. The TFP will
accept time code in either amplitude modulated (AM) or DC Level Shift (DCLS) form. AM time code is
a sinusoidal analog signal that is amplitude modulated with the time data. DCLS is simply the envelope
of the modulated time code and is a digital signal. Most time codes provide both major time (days,
hours, minutes, and seconds) and minor time (subseconds) to the card. Some IRIG time codes (e.g.,
IEEE1344) and GPS (if equipped) provide year information.
Mode 1 (Free Running Mode)
In Free Running Mode, no external timing source is used and the TFP oscillator is allowed to free-run.
The user must set major time manually. The Major Time is selected via the dual port RAM interface
as described in "Command 0x11: Set Time Register Format" on page 41, using command 11. Free
Run mode allows the user to perform timing tests when an external timing source is unavailable.
Mode 2 (External 1 PPS Mode)
In External 1 PPS Mode, the TFP synchronizes its oscillator to a user-supplied 1 PPS signal. The
user must set major time manually. The Major Time is selected via the dual-port RAM interface as
described in "Command 0x11: Set Time Register Format" on page 41 Chapter 1.5, using command
11. The External 1PPS Mode will not indicate locked status to the External 1PPS reference without
first being synchronized to a time reference that includes time of day information (Time Code or
GPS). Please note that the TFM will always synchronize to the External 1PPS when selected, but if
the card has not been previously synchronized by Time Code or GPS, the Tracking, Phase and
Frequency Status information will not be valid in External 1PPS mode.
Mode 3 (RTC)
In the Real Time Clock (RTC) mode, the TFP receives its major time via the RTC and operates as a
Generator (no input reference).
Mode 6 (GPS) - bc637PCI-V2 and bc637PCIe
In GPS Mode, like Time Code Mode, both major and minor times are derived from the timing source.
In addition to time, other information is available from the GPS system such as position and velocity.
This mode requires the use of a GPS antenna that has an unobstructed view of the sky. Note that the
antenna location is important because the GPS receiver must initially acquire and track at least four
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