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T7234

Compliance with the New ETSI PSD Requirement

Agere -> LSI Corporation 

T7256 Single-Chip NT1 (SCNT1) Transceiver

Data Sheet

January 1998

Functional Overview (continued)

When the T7256 is powered on and there is no activity

on the S/T- or U-interfaces (i.e., no pending activation

request), it automatically enters a low-power IDLE

mode in which it consumes an average of 35 mW.

This mode is exited automatically when an activation or

U maintenance request occurs from either the micro-

processor or the S/T- or U-interfaces. The T7256 pro-

vides a board-level test capability that allows functional

verification. Finally, an LED driver output indicates the

status of the device during operation.

U-Interface Frame Structure

Data is transmitted over the U-interface in 240-bit

groups called U frames. Each U frame consists of an

18-bit synchronization word or inverted synchronization

word (SW or ISW), 12 blocks of 2B+D data (216 bits),

and six overhead bits (M bits). A U-interface super-

frame consists of eight U frames grouped together. The

beginning of a U superframe is indicated by the

inverted sync word (ISW). The six overhead bits (M1—

M6) from each of the eight U frames, when taken

together, form the 48 M bits. Figure 4 shows how U

frames, superframes, and M bits are arranged.

Of the 48 M bits, 24 bits form the embedded operations

channel (eoc) for sending messages from the LT to the

NT and responses from the NT to the LT. There are two

eoc messages per superframe with 12 bits per eoc

message (eoc1 and eoc2). Another 12 bits serve as U-

interface control and status bits (UCS). The last 12 bits

form the cyclic redundancy check (CRC) which is cal-

culated over the 2B+D data and the M4 bits of the pre-

vious superframe. Figure 5 and Table 2 show the

different groups of bits in the superframe.

ISW[18]

U1

U2

U-FRAME SPAN = 1.5 ms

(2B+D) x 12 [ 216 bits]

M[6]

U-SUPERFRAME SPAN = 12 ms

U3

U4

U5

U6

U7

U8

U-INTERFACE M BITS [48]

Figure 4. U-Interface Frame and Superframe

5-2476 (C)

12

Lucent Technologies Inc.

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