ds3102 Maxim Integrated Products, Inc., ds3102 Datasheet - Page 25

• Manufacturer Part Number: ds3102
• Description: Stratum 3 Timing Card Ic With Synchronous Ethernet Support
• Manufacturer: Maxim Integrated Products, Inc.

____________________________________________________________________________________________ DS3102
In external reference switching mode the device is simply a clock switch, and the T0 DPLL is forced to lock onto the
selected reference whether it is valid. Unlike forced reference selection (Section 7.6.3) this mode controls the
PTAB1:SELREF field directly and is, therefore, not affected by the state of the MCR3:REVERT bit. During external
reference switching mode, only PTAB1:SELREF is affected; the REF1, REF2, and REF3 fields in the
PTAB
registers continue to indicate the highest, second-highest, and third-highest priority valid inputs chosen by the
automatic selection logic. External reference switching mode only affects the T0 DPLL.
7.6.6 Output Clock Phase Continuity During Reference Switching
If phase build-out is enabled (PBOEN = 1 in MCR10) or the DPLL frequency limit (DLIMIT) is set to less than
±30ppm, the device always complies with the GR-1244-CORE requirement that the rate of phase change must be
less than 81ns per 1.326ms during reference switching.
Rev: 012108
25 of 141