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IDT82P2288
OCTAL T1/E1/J1 LONG HAUL / SHORT HAUL TRANSCEIVER
Functional Description
101
March 04, 2009
3.24.1.2 E1 Mode
In E1 applications, the waveform template is shown in
Figure 34,which meets G.703, and it is measured on the near line side as shown in
Figure 34. E1 Waveform Template
Figure 35. E1 Pulse Template Measurement Circuit
To meet the template, two preset waveform templates are provided
corresponding to two kinds of cable impedance. The selection is made
by the PULS[3:0] bits. In internal impedance matching mode, if the cable
impedance is 75
, the PULS[3:0] bits should be set to ‘0000’; if the
cable impedance is 120
, the PULS[3:0] bits should be set to ‘0001’. In
external impedance matching mode, for both 75
and 120 cable
impedance, the PULS[3:0] bits should be set to ‘0001’.
3.24.2 LINE BUILD OUT (LBO) (T1 ONLY)
In long haul applications, the output on the TTIPn/TRINGn pins
should be attenuated before transmission to prevent the cross-talk in the
far end. Three LBOs are used to implement the pulse attenuation. Four
grades of attenuation with each step of 7.5 dB are specified in the FCC
Part 68 Regulations. The attenuation grade is selected by the PULS[3:0]
3.24.3 USER-PROGRAMMABLE ARBITRARY WAVEFORM
User-programmable arbitrary waveform can be used in both short
haul applications and long haul applications if the PULS[3:0] bits are set
to ‘11XX’ in the corresponding link. This allows the transmitter perfor-
mance to be tuned for a wide variety of line condition or special applica-
tion.
Each pulse shape can extend up to 4 UIs (Unit Interval) addressed
by the UI[1:0] bits, and each UI is divided into 16 sub-phases addressed
by the SAMP[3:0] bits. The pulse amplitude of each phase is repre-
sented by a binary byte, within the range from +63 to -63, stored in the
WDAT[6:0] bits in signed magnitude form. The maximum number +63
(D) represents the positive maximum amplitude of the transmit pulse
while the most negative number -63 (D) represents the maximum nega-
tive amplitude of the transmit pulse. Thus, up to 64 bytes are used. For
each channel, a 64 bytes RAM is available.
There are twelve standard templates which are stored in a local
ROM. One of them can be selected as reference and made some
changes to get the desired waveform.
To do this, the first step is to choose a set of waveform value, which
is the most similar to the desired pulse shape, from the following 12
the standard scaling value of each of the 12 templates.
Modifying the corresponding sample data can get the desired
transmit pulse shape. By increasing or decreasing by ‘1’ from the stan-
dard value in the SCAL[5:0] bits, the pulse amplitude can be scaled up
Table 60: PULS[3:0] Setting In T1/J1 Mode
Cable Configuration
PULS[3:0]
T1 - 0 ~ 133 ft
0 0 1 0
T1 - 133 ~ 266 ft
0 0 1 1
T1 - 266 ~ 399 ft
0 1 0 0
T1 - 399 ~ 533 ft
0 1 0 1
T1 - 533 ~ 655 ft
0 1 1 0
J1 - 0 ~ 655 ft
0 0 1 0
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
1.20
N
ormalized
A
m
plitude
Time In Unit Intervals
IDT82P2288
VOUT
RLOAD
TTIPn
TRINGn
Note: RLOAD = 75
or 120 (+ 5%)
Table 61: LBO PULS[3:0] Setting In T1 Mode
Cable Configuration
PULS[3:0]
0 dB LBO
0 0 1 0
-7.5 dB LBO
1 0 0 1
-15.0 dB LBO
1 0 1 0
-22.5 dB LBO
1 0 1 1