8 clock output stability considerations, 1 output switching, Cs2000-otp – Cirrus Logic CS2000-OTP User Manual
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CS2000-OTP
20
DS758F2
5.7.2.3
M2 Configured as Auto Fractional-N Source Selection Disable
If M2Config[2:0] is set to ‘100’, M2 becomes a disable pin for the auto fractional-N source selection
functionality. If auto fractional-N source selection is enabled (see
), driving
M2 ‘high’ will disable the auto fractional-N source selection and revert control over the fractional-N
source to the FracNSrc modal parameter, regardless of the LockClk[1:0] modal parameter and the
presence of a clock on CLK_IN. If auto fractional-N source selection is not enabled, toggling M2 will
have no effect in this case.
5.7.2.4
M2 Configured as Fractional-N Source Select
If M2Config[2:0] is set to ‘110’, M2 becomes the Fractional-N Source Select pin and will override
the FracNSrc modal parameter. It should be noted that overriding FracNSrc has no effect when
auto clock switching is enabled (see
). If M2 is driven ‘low’, the fractional-
N value will be the Static Ratio sourced directly from R
EFF
for Frequency Synthesizer Mode. If M2
is driven ‘high’ the fractional-N value will be the Dynamic Ratio sourced from the Digital PLL for Hy-
brid PLL Mode.
5.7.2.5
M2 Configured as AuxOutSrc Override
If M2Config[2:0] is set to ‘111’, M2 when driven ‘high’ will override the AuxOutSrc[1:0] modal pa-
rameter and force the AUX_OUT source to PLL Clock Output. When M2 is driven ‘low’, AUX_OUT
will function according to AuxOutSrc[1:0].
5.8
Clock Output Stability Considerations
5.8.1
Output Switching
The CS2000-OTP is designed such that re-configuration of the clock routing functions do not result in a
partial clock period on any of the active outputs (CLK_OUT and/or AUX_OUT). In particular, enabling or
disabling an output, changing the auxiliary output source between REF_CLK and CLK_OUT, changing
between Frequency Synthesizer and Hybrid PLL Mode, and the automatic disabling of the output(s) dur-
ing unlock will not cause a runt or partial clock period.
The following exceptions/limitations exist:
•
Enabling/disabling AUX_OUT when AuxOutSrc[1:0] = 11 (unlock indicator).
•
Switching AuxOutSrc[1:0] to or from 01 (CLK_IN) and to or from 11 (unlock indicator)
(Transitions between AuxOutSrc[1:0] = [00,10] will not produce a glitch).
When any of these exceptions occur, a partial clock period on the output may result.