GS4915 Data Sheet
3.4.2 Bypass Modes
The bypass mode of the device is determined by the setting of the external
AUTOBYPASS and BYPASS pins.
Table 3-3: GS4915 Bypass Modes
AUTOBYPASS
BYPASS
Bypass Mode
0
X
0
1
Autobypass Mode
Forced Output Mode
Manual Bypass Mode
1
1
NOTE: 'X' indicates a "don't care" condition.
Autobypass Mode
When AUTOBYPASS is LOW, the device will operate in Autobypass mode. In this
mode, the GS4915 will bypass its cleaning stage and pass the selected input clock
signal directly to the output whenever LOCK is LOW.
Manual Bypass Mode
When AUTOBYPASS and BYPASS are both HIGH, the GS4915 will operate in
Manual Bypass Mode. In this mode, the GS4915 will bypass its cleaning stage and
pass the selected input clock signal directly to the output.
NOTE: If operating in Manual Bypass mode, the LOCK output pin should be
ignored. Depending on the set frequency mode of the device and the detected
frequency of the selected input clock, the cleaning PLL of the device may achieve
lock and so may set the LOCK pin HIGH; however, the output clock will always be
a copy of the input clock, and NOT the cleaned clock.
Forced Output Mode
If AUTOBYPASS is HIGH and BYPASS is set LOW, the device will operate in
Forced Output mode. In this mode, the cleaning stage of the device is never
bypassed, and so the output clock will always be the clock output by the device's
PLL, even in an unlocked condition.
When LOCK is HIGH, the output clock will be low-jitter and locked to the selected
input clock. But when LOCK is LOW in Forced Output mode, the output clock
should not be used.
39145 - 3 November 2007
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