
XRT8001
39
Rev. 1.01
9.0 Generating a 1.544MHz clock signal via the
“CLK1/CLK2” outputs from either a 1.544MHz, or a
2.048MHz clock signal
When approaching this problem, be aware that the
XRT8001 WAN Clock can be configured to accept a
2.048MHz clock signal via the “FIN” input pin and
generate a 1.544MHz clock signal. However, the
XRT8001 WAN Clock cannot be configured to accept
a 1.544MHz clock signal, and generate a 1.544MHz
clock signal.
Also, note the XRT8001 WAN Clock can be configured
to accept a 2.048MHz clock signal (via the “FIN” input)
and generate a 1.544MHz clock signal if it configured
to operate in the “E1 to T1 Forward/Master” Mode. The
XRT8001 can similarly be configured to accept an
8kHz clock signal (via the same “FIN” input pin) and
generate a 1.544MHz clock signal if it is configured to
operate in the “Reverse/Slave” Mode.
Based upon these two points, the necessary circuitry
(in order to synthesize a 1.544MHz clock signal, from
either a 1.544MHz or a 2.048MHz clock signal) can be
achieved by the approach shown below in a block
diagram.
193
2 : 1 MUX
SE
L
FIN
MSB
CLK1
CLK2
XRT8001 WAN Clock
1.544MHz or 2.048MHz Clock Signal
E1/T1* SELECT
1.544MHz
1.544MHz
8kHz
2.048MHz or 8kHz Clock Signal
Divide by
SEL
In Figure 23, the 1.544MHz or 2.048MHz input clock
signal is routed to two locations.
One of the inputs of a “2:1 MUX”.
The “CU” input of a “Divide-by-193” Block.
Figure 23 also includes a digital “E1/T1* SELECT”
signal. This signal is connected to both the “SEL” input
of the “2:1 MUX” and the “MSB” input of the XRT8001
WAN Clock. The basic idea behind this schematic is
as follows:
1. If the incoming clock signal (from the T1/E1 LIU for
example) is a 1.544MHz clock signal, then this signal
will be divided by 193. As it passes through the “Divide-
by-193” block a 8kHz clock signal is generated. This
8kHz clock signal will be applied to one of the inputs to
the “2:1 MUX”.
(
NOTE:
A 1.544MHz clock signal is
applied to the other input to the “2:1 MUX”).
In this case, the user must set the “E1/T1* SELECT”
signal to “LOW”, order to select “T1 rates” (1.544MHz).
By doing this, the 8kHz output from the “Divide-by-193”
block is selected and will be applied to the “FIN” input
of the XRT8001; and the XRT8001 will be configured to
operate in the “Slave” Mode.
At this point, the user will need to execute the appro-
priate steps in order to configure the XRT8001 into the
“Reverse-Slave” Mode.
2. If the incoming clock signal (from the T1/E1 LIU) is
a 2.048MHz clock signal, then this signal will also be
divided by 193. As it passes through the “Divide-by-
193” block, it generates a clock signal of a strange (and
undesirable frequency). This clock signal will be
applied to one of the inputs to the “2:1 MUX” (
NOTE
:
The 2.048MHz clock will also be applied to the other
input of the “2:1 MUX
).
Figure 23: Synthesizing a 1.544MHz clock signal from a 1.544MHz or 2.048MHz clock