Symmetricom TimeHub 5500 User Manual

097-55501-01 Revision M – January 2009 TimeHub 5500 User’s Guide 37
Chapter 1 Description
Passthrough Mode
 There are likely to be brief phase-hits on the outputs when entering and exiting
Passthrough mode.
 If an Expansion shelf is connected to the Master it also will operate in
Passthrough mode.
If the Management and Clock cards contain firmware version 4315B or later AND
have hardware revision B or later, then the Passthrough capability is as follows:
 Passthrough functions when the shelf is configured as either master or remote.
As should be expected, for a remote shelf the timing references must be CC1
inputs. For a master shelf the timing references must be DS1 or 5/10 MHz inputs.
 Phase-alignment between input and output is maintained during the transition
into Passthrough from normal operation, while in Passthrough, and during the
exit from Passthrough back to normal operation.
While this feature applies to both Master and Remote shelves, the easiest way to
understand it is to consider a Remote shelf that is timing a CC input prior to entering
Passthrough mode. Prior to Passthrough mode, the alignment of the active CC
input and any output CC will be nearly perfect. If you observed the positive bi-polar
violations on the input and any CC output on an oscilloscope, you would see that
they are completely aligned. The Passthrough feature maintains this alignment
while entering into Passthrough, while in Passthrough, and when exiting from
Passthrough back to normal operation (which would occur when a Clock card is
re-inserted). Thus, the phase alignment between input and output is never lost
during the entire Passthrough episode.
If an Expansion shelf is connected, it also operates in Passthrough mode, but its
behavior depends on the firmware revision of the Expansion Controller cards:
 If an Expansion Controller card contains version A firmware, outputs from that
Expansion shelf do not maintain the pre-Passthrough phase-alignment while in
Passthrough mode of operation.
 If an Expansion Controller card contains version B (or later) firmware, outputs
from that Expansion shelf will maintain pre-Passthrough phase-alignment while
in Passthrough mode of operation.
Note: Since Passthrough is not a normal operating mode, it should
not be routinely used. It is intended to provide a mechanism to “keep
alive” the outputs in a situation when both Clock cards are
inadvertently removed. The timing performance when in Passthrough
mode cannot be assured.

Symmetricom TimeHub 5500 Specifications

General

Brand	Symmetricom
Model	TimeHub 5500
Category	Data Loggers
Language	English