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CS61577 Datasheet(PDF) 10 Page - Cirrus Logic

Part No. CS61577
Description  T1/E1 Line Interface
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Maker  CIRRUS [Cirrus Logic]
Homepage  http://www.cirrus.com
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Transmitter
The transmitter takes digital T1 or E1 input data
and drives appropriately shaped bipolar pulses
onto a transmission line through a 1:2 trans-
former. The transmit data (TPOS & TNEG or
TDATA) is supplied synchronously and sampled
on the falling edge of the input clock, TCLK.
Either T1 (DSX-1 or Network Interface) or E1
CCITT G.703 pulse shapes may be selected.
Pulse shaping and signal level are controlled by
"line length select" inputs as shown in Table 3.
For T1 DSX-1 applications, line lengths from 0 to
655 feet (as measured from the transmitter to the
DSX-1 cross connect) may be selected. The five
partition arrangement in Table 3 meets ANSI
T1.102 and AT&T CB-119 requirements when
using #22 ABAM cable. A typical output pulse is
shown in Figure 8. These pulse settings can also
be used to meet CCITT pulse shape requirements
for 1.544 MHz operation.
For T1 Network Interface applications, two addi-
tional options are provided. Note that the optimal
pulse width for Part 68 (324 ns) is narrower than
the optimal pulse width for DSX-1 (350 ns). The
CS61577 automatically adjusts the pulse width
based upon the "line length" selection made.
The E1 G.703 pulse shape is supported with line
length
selections
LEN 2/ 1/0=0/0/0
or
LEN 2/1 /0= 0/0 /1. As wi th th e CS61 574 ,
LEN2/1/0=0/0/0 supports the 120
Ω, 3 V output
option without external series resistors, but will
also support the 75
Ω, 2.37 V output option with
an external 4.4
Ω resistor in series with TTIP or
TRING. The new LEN2/1/0=0/0/1 code supports
the 75
Ω, 2.37 V output option without external
series resistors allowing for software selection be-
tween the two E1 output options. The pulse width
will meet the G.703 pulse shape template shown
in Figure 9, and specified in Table 4.
The CS61577 will detect a static TCLK, and will
force TTIP and TRING low to prevent transmis-
sion when data is not present. When any transmit
control pin (TAOS, LEN0-2 or LLOOP) is tog-
gled, the transmitter outputs will require
approximately 22 bit periods to stabilize. The
transmitter will take longer to stabilize when
RLOOP is selected because the timing circuitry
must adjust to the new frequency.
500
1.0
0.5
0
-0.5
0
250
750
1000
NORMALIZED
AMPLITUDE
AT&T CB 119
SPECIFICATIONS
PULSE SHAPE
OUTPUT
TIME (nanoseconds)
ANSI T1.102,
Figure 8. Typical Pulse Shape at DSX-1 Cross Connect
0
1
1
0-133 FEET
DSX-1
ABAM
(AT&T 600B
or 600C)
100
133-266 FEET
101
266-399 FEET
110
399-533 FEET
111
533-655 FEET
000
75
Ω (with 4.4 Ω
resistor) & 120
Ω
E1
CCITT G.703
001
75
Ω (without
4.4
Ω resistor)
0
1
0
FCC PART 68, OPT. A NETWORK
INTERFACE
011
ANSI T1.403
Table 3. Line Length Selection
CS61577
10
DS155F




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