2.0 Circuit Description
Bt8370/8375/8376
2.9 Transmit Line Interface Unit
Fully Integrated T1/E1 Framer and Line Interface
The pulse shape block receives P and N rail NRZ data. For each mark, it
produces a set of eight 6-bit values which define the pulse shape to be transmitted,
as illustrated in Figure 2-39. One of eight preprogrammed pulse shapes is
selected via the Transmit LIU Configuration register [TLIU_CR; addr 068]. The
TLIU control circuit downloads the code values associated with the selected pulse
shape from the ROM to the Transmit Pulse Shape Configuration registers
[SHAPE; addr 060–067], whenever the TLIU register is written to or when the
device is reset. The SHAPE registers can be directly accessed via the
microprocessor interface when a custom pulse shape is desired.
NOTE: Any modification to the TLIU register initiates another download to the
SHAPE registers. The data stored in the pulse shape ROM and the SHAPE
registers is 5-bit magnitude only.
The TLIU control circuit converts the 5-bit magnitude to 6-bit 2's complement
data. The first 4 code values of the pulse (first half of the symbol) are forced to be
positive, and the last 4 values (last half of the symbol) are forced to be negative,
with respect to output pulse polarity.
Figure 2-39. Digitized AMI Pulse Shape
TCKO
8TCKO
ShapeAddr [060–067]
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0 1 2 3 4 5 6 7 0
Shape Data
Magnitude
0x00–0x1F
Digitized
AMI Pulses
Positive Pulse
No Pulse
Negative Pulse
2-74
Conexant
N8370DSE
CONEXANT [ CONEXANT SYSTEMS, INC ]
