CDB61574 Cirrus Logic, Inc., CDB61574 Datasheet - Page 10

• Manufacturer Part Number: CDB61574
• Description: T1/e1 LINE Interface
• Manufacturer: Cirrus Logic, Inc.

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.
10
LEN2 LEN1 LEN0
0
1
1
1
1
0
0
0
0
1
0
0
1
1
0
0
1
1
Table 3. Line Length Selection
1
0
1
0
1
0
1
0
1
FCC PART 68, OPT. A NETWORK
Option Selected
resistor) & 120
75
133-266 FEET
266-399 FEET
399-533 FEET
533-655 FEET
4.4
75
ANSI T1.403
0-133 FEET
(with 4.4
(without
resistor)
CCITT G.703
INTERFACE
Application
(AT&T 600B
or 600C)
DSX-1
ABAM
E1
The E1 G.703 pulse shape is supported with line
length
LEN2/1/0=0/0/1. As with the CS61574,
LEN2/1/0=0/0/0 supports the 120
option without external series resistors, but will
also support the 75
an external 4.4
TRING. The new LEN2/1/0=0/0/1 code supports
the 75
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.
-0.5
Figure 8. Typical Pulse Shape at DSX-1 Cross Connect
1.0
0.5
0
0
NORMALIZED
AMPLITUDE
, 2.37 V output option without external
selections
250
PULSE SHAPE
resistor in series with TTIP or
OUTPUT
TIME (nanoseconds)
, 2.37 V output option with
500
LEN2/1/0=0/0/0
ANSI T1.102,
AT&T CB 119
SPECIFICATIONS
750
CS61577
, 3 V output
DS155PP2
1000
or