Silicon Laboratories SI5375 - Manual (Page 88)

S i 5 3 x x - R M
88 Rev. 1.2
6.11.6. C1B, C2B, C3B, ALRMOUT (Si5368 [CK_CONFIG_REG = 1])
The generation of alarms on the C1B, C2B, C3B, and ALRMOUT outputs is a function of the input clock
configuration, and the frequency offset alarm enable as shown in Table 44. The LOSn_INT and FOSn_INT signals
are the raw outputs of the alarm monitors. These appear directly in the device status registers. Sticky versions of
these bits (LOSn_FLG, FOSn_FLG) drive the output interrupt and can be individually masked. Since, CKIN3 and
CKIN4 are configured as frame sync inputs (CK_CONFIG_REG = 1), ALRMOUT functions as the alignment alarm
output (ALIGN_INT) as described in Section “6.8. Frame Synchronization Realignment (Si5368 and
CK_CONFIG_REG = 1)”. The equations below assume that the output alarm is active high; however, the active
polarity is selectable via the CK_BAD_POL bit.
Operation of the C1B, C2B, C3B, and ALRMOUT pins is enabled based on setting the C1B_PIN, C2B_PIN,
C3B_PIN, and ALRMOUT_PIN register bits. Otherwise, the pin will tri-state. Also, if INT_PIN = 1, the interrupt
functionality will override the appearance of ALRMOUT at the output even if ALRMOUT_PIN = 1.
Once an LOS or FOS alarm is asserted for one of the input clocks, it is held high until the input clock is validated
over a designated time period. The validation time is programmable via the VALTIME[1:0] register bits as described
in the data sheet. If another error condition on the same input clock is detected during the validation time then the
alarm remains asserted and the validation time starts over.
Note that hitless switching between input clocks applies only when the input clock validation time
VALTIME[1:0] = 01 or higher.
Table 43. Alarm Output Logic Equations (Si5367, Si5368, and Si5369 [CONFIG_REG = 0])
FOS_EN Alarm Output Equations
0
(Disables FOS)
C1B = LOS1_INT
C2B = LOS2_INT
C3B = LOS3_INT
ALRMOUT = LOS4_INT
1 C1B = LOS1_INT or FOS1_INT
C2B = LOS2_INT or FOS2_INT
C3B = LOS3_INT or FOS3_INT
ALRMOUT = LOS4_INT or FOS4_INT
Table 44. Alarm Output Logic Equations [Si5368 and CKCONFIG_REG = 1]
FOS_EN Alarm Output Equations
0
(Disables FOS)
C1B = LOS1_INT or (LOS3_INT and FSYNC_SWTCH_REG)
C2B = LOS2_INT or (LOS4_INT and FSYNC_SWTCH_REG)
C3B tri-state,
ALRMOUT = ALIGN_INT
1 C1B = LOS1_INT or (LOS3_INT and FSYNC_SWTCH_REG) or FOS-
1_INT
C2B = LOS2_INT or (LOS4_INT and FSYNC_SWTCH_REG) or FOS-
2_INT
C3B tri-state,
ALRMOUT = ALIGN_INT