STC3800 Datasheet, PDF (37/48 Pages) Connor-Winfield Corporation – INTEGRATED - STRATUM 3E TIMING SOURCE

Application Notes continued
Hold Over History Accumulation and Maintenance – Hold Over history accumulation and maintenance may be
controlled in greater detail if register bus access to the device is provided. Hold Over history accumulation and control
encompasses three device internal registers, three bus access registers for control and access, and two status bits in
the DPLL_Status register.
Holdover History
accumulation register
Active Holdover
History
Backup Holdover
History
Once lock has been achieved, Hold Over history is compiled in the accumulation register. It is transferred to the Active
Hold Over history when it is ready (typically in about 15 minutes). The “Holdover Available” bit and output pin are set to
“1”. From then on, the Active Hold Over history is continually updated and kept in sync with the Hold Over history
accumulation register. (See Figure 12).
0x25
0x26
0x27
0x11
Hold Over History Access and Control Registers
Table 11
History_Policy
Sets policy for Hold Over history accumulation: “Rebuild” or “Continue”
History_Cmd
Save, restore, and flush commands for Hold over history
Hold Over_Time
Indicates the time since entering the Hold Over state
DPLL_Status
Bits3 and 4: “Hold Over Available” and “Hold Over Build Complete”
Preliminary Data Sheet #: TM061 Page 37 of 48 Rev: P06 Date: 11/22/04
© Copyright 2001 The Connor-Winfield Corp. All Rights Reserved Specifications subject to change without notice