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參數(shù)資料
| 型號(hào)： | T7234A |
| 英文描述： | Compliance with the New ETSI PSD Requirement |
| 中文描述： | 符合新的ETSI PSD的要求 |
| 文件頁(yè)數(shù)： | 92/116頁(yè) |
| 文件大?。?/td> | 1056K |
| 代理商： | T7234A |
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Data Sheet
January 1998
T7256 Single-Chip NT1 (SCNT1) Transceiver
88
Lucent Technologies Inc.
Questions and Answers
(continued)
S/T-Interface
Q30:
What is the S/T transformer’s inductance
A30:
For Lucent transformers 2768A or 2776, a mini-
mum inductance of 22 mH is guaranteed.
Q31:
We are trying to test the S/T side of our T7256-
based NT1 using a Siemens K1403 ISDN tester.
The tester is not able to sync up to the NT1. Can
you explain this behavior
A31:
Check the connector wiring of the S/T-interface.
In the January 1995 T7256 data sheet, the
pinouts of the RJ-45 S/T connector (J1) were
shown incorrectly. The ones shown are for a TE.
The correct (i.e., NT) pinouts are listed in the cur-
rent T7256 data sheet (swap pins 3 and 6 with
pins 4 and 5, respectively). If the pinout is wrong
as just described, the Siemens K1403 will not
sync up to the S/T-interface.
Q32:
Can the S/T-interface leads be short-circuited
together without harming the device
A32:
Yes, this will not cause any harm to the device.
Q33:
What is the common-mode rejection of the S/T
receiver
A33:
The common-mode rejection of the S/T receiver
is 400 mV. Refer to the Electrical Characteristics
described in the data sheet.
Q34:
I notice that the application note entitled Design
an S/T Line Interface Circuitry Using the T7250C/
T7259 recommends relays on both the transmit-
ter and receiver outputs that disconnect the
device when power is removed from the chip. Is
this necessary for an NT using the T7256
A34:
The relay on the TE transmitter output is neces-
sary to pass the peak current test (ITU-T I.430
Section 8.5.1.2 and ANSI T1.605-1991, section
9.5.1.2) when the TE is powered down. For the
NT, there is no equivalent test, so the relay is not
necessary. The relay on the TE receiver input is
also necessary to pass the peak current test
(ITU-T I.430 Sections 8.5.1.2 and 8.6.1.1, and
ANSI T1.605-1991 Sections 9.5.1.2 and 9.6.1.1).
For the NT, however, there is enough margin in
the line interface capacitance circuitry such that
the peak current requirement (ITU-T I.430 Sec-
tion 8.6.1.2 and ANSI T1.605-1991 Section
9.6.1.2) can be met without using relays. This
assumes, of course, that sound layout practices
have been applied to keep parasitic capacitance
of the line interface circuitry to a minimum (of pri-
mary importance is making sure there is no
ground plane under the S/T line interface). The
reason the TE needs a relay on its receiver is that
the TE tests assume a 350 pF cord connected to
the line, and this extra capacitance can cause the
peak current requirement to be exceeded. So
even though the NT peak current requirement
is slightly more stringent (0.5 mA as opposed to
0.6 mA), the TE peak current test is the most diffi-
cult to meet due to the 350 pF cord capacitance.
Q35:
The T7256 reference design in Figure 21 shows
100
termination resistors in parallel with a sec-
ond pair of optional 100
resistors that can be
inserted or removed by installing/removing jump-
ers from JMP1 and JMP2. What is the purpose of
this second pair of resistors
A35:
Typically, a TE or group of TEs connected to an
NT1 will have a 100
termination located at the
interface point of the TE farthest from the NT1
(refer to ITU-T I.430 Figure 2 and Section 4 or
T1.605 Figure 2 and Section 5). However, in
some cases it may be desirable to operate an
NT1 with a TE that does not provide the 100
termination impedance. In this case, the provi-
sional 100
resistors shown in Figure 21 may be
installed to provide the extra termination imped-
ance required.
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