CHAPTER FOUR
4-2
bc635VME/bc350VXI Time and Frequency Processor (Rev. E)
Symmetricom Inc
4.1.1 PACKET “A” SELECT TFP OPERATIONAL MODE
This packet contains a single data byte (zero through seven) which defines the TFP operational
mode. The mode is saved in the battery backed RAM. The modes are enumerated below.
Mode 0 (Zero) Time Code Decoding Mode
The TFP uses an input timecode as the timing reference. See packet “H” for time codes
supported. Both modulated carrier and DC level shift formats are supported (DC level shift is
not supported for 2137 or XR3 codes). The TFP locks its crystal oscillator to the input code rate.
The oscillator has a control range of
±
30PPM for the standard DPI version, and
±
2PPM for the
optional oven version. If the input code is outside these limits, the TPF will exhibit periodic
slips (if the TFP reference deviates from the input source by more than
±
1 millisecond, a forced
jamsync is performed). If the input code is lost or removed, the TFP will continue to “flywheel”
at the last known code rate. Typical accuracy is five parts in 10
7
(two milliseconds of drift per
hour).
Mode 1 Free Running Mode
This mode is virtually the same as Mode 2. Without a 1pps input the TFP runs at the last known
oscillator frequency. Major time can be set with the “B” packet. The TFP timebase can be
adjusted with packet “D.”
Mode 2 External 1 pps Mode
The TFP synchronizes to the signal on the 1pps input. Major time can be loaded with the “B”
packet. The acquisition range is the same as described in mode zero.
Mode 3 Real Time Clock Mode
The TFP synchronizes to the onboard real time clock (RTC) IC, and the major time is also
derived from the clock IC. The RTC is battery backed. This mode is not recommended when
using the oven oscillator because the accuracy of the RTC is not high enough to ensure that the
oven will be able to track it with slippages. See Mode 0 (zero) description.
Mode 4 Digital Sync Mode
This mode is not implemented.
Mode 5 GPS Mode with GPS Receiver Onboard (Obsolete)
The TFP only supports this mode in the bc635VME/bc357VXI configuration. It is currently
available only in a double wide 6U form factor.
Mode 6 GPS Mode with GPS Receiver Located in the Antenna
This is an optional mode available with the bc637VME/bc357VXI configuration. It is described
in a separate User's Guide.
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