CPC324 Functional Blocks
35
The MT90866 has two interrupts that are associated with the detection of the primary or
secondary reference loss. They are FAIL_PRI and FAIL_SEC. They are connected directly to
the AMCC 440GX’s external interrupt inputs.
CT Clock and Frame Monitor Circuits
These monitor circuits check the period of the CTC8_A and the CTC8_B clocks and the
CTFRMA# and CTFRMB# frame pulses. According to the H.110 signal specification, the C8
period is 122 ns with a tolerance of
±
35 ns measured between rising edges. If C8 falls outside
the range of [87 ns,157 ns], the clock is rejected and the fail signal (FAIL_A or FAIL_B)
becomes high. The frame pulse period is measured with respect to the C8 clock. The frame
pulse period must have exactly 1024 C8 cycles. Otherwise, the fail signal (FAILA_INT or
FAILB_INT) becomes high. They are connected directly to the AMCC 440GX’s external
interrupt inputs.
External Reference Clock Sources
These sources include any of the recovered clocks from the IDT82P2288 framer’s receivers or
an on-board 1.544 MHz, 25 ppm crystal oscillator. The recovered clocks and oscillator are
mapped to the MT90866’s local reference source (LREF0-6) inputs through CPLD as shown in
Table 2-6, “MT90866 Local Reference Sources,”
below.
H.110 Clock Operating Modes
The MT90866 contains clock distribution and control circuitry that supports both master and
slave modes of H.110 operation. The H.110 switch provides primary and secondary clock and
frame synchronization sources for the local TDM streams. The synchronization is distributed to
all of the local TDM devices as described in the previous sections. H.110 backplane clocks
CT_C8_A and CT_C8_B are supported at 8 MHz operation exclusively. Local clocks are
supported at 8 MHz operation exclusively.
Table 2-6:
MT90866 Local Reference Sources
MT90866 Input Signal
Referenced Input
LREF0
FRAMER A reference output A
LREF1
FRAMER A reference output B
LREF2
FRAMER B reference output A
LREF3
FRAMER B reference output B
LREF4
FRAMER C reference output A
LREF5
FRAMER C reference output B
LREF6
On-board 1.544 MHz crystal oscillator
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