TP3420AV datasheet(16/32 Pages) NSC

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Functional Description (Continued)

Contiguous B1+B2 (128 kbit/s) digital loopback (LBB1,

LBB2) in TEM mode and in NT/TES modes if FSa is

phase synchronous with FSb.

Contiguous B1+B2+D (144 kbit/s) digital loopback (LBD)

in TEM mode and in NT/TES modes if FSa is phase syn-

chronous with FSb.

B1 line loopback (using LBL1) with any FSa/FSb rela-

tionship in all TE or NT modes.

B2 line loopback (using LBL2) with any FSa/FSb rela-

tionship in all TE nor NT modes.

Contiguous B1+B2 (128 kbit/s pipe) line loopback

(LBL1, LBL2) with equal delay, available in TEM mode,

and in NT/TES modes if FSa is phase synchronous with

FSb.

Note that a line loopback for the D channel is not specified in

the CCITT I.430 or the T1-605 specification, to ensure that D

channel signaling is transparently passed end-to-end.

ACTIVATION/DEACTIVATION: TP3420A IN NT MODE

Activation (i.e. transmission and loop synchronization) may

be initiated from either end of the loop.

Activation initiated from the NT: to initiate Activation from the

NT, the TP3420A must be powered up, using a PUP com-

mand, followed (Note 12) by an AR instruction to the Control

a, must be

present at this time. The device then begins to send data

framed as INFO 2 type, in which bits in the B, D and D-echo

channels are set to binary 0. These frames are detected by

the TE, which replies with data framed as INFO 3 type, syn-

chronized to received frames. A flywheel circuit in the

TP3420A NT searches for 3 consecutive correctly formatted

receive frames to acquire frame synchronization. If Multi-

framing is enabled (MIE), 60 correct frames (3 multiframes)

are required to achieve full loop synchronization. When it is

correctly in sync with received frames, the NT interrupts the

control processor with Status Indication type AP. A second

AR command is required to cause the NT to send INFO 4

frames, in which the B and D channels are enabled for trans-

mission; Status Indication type AI is then set, and the INT

output is pulled low to indicate Activation complete.

Note 12: A delay of

≥2 msecs is recommended to ensure that all internal cir-

cuits have settled.

Activation initiated by a TE: when Activation is initiated by a

TE, the TP3420A in NT mode will detect the incoming INFO

1 signal and, if it is powered-down will pull the LSD pin and

INT low, either of which can be used to “wake-up” a micro-

processor. A PUP command must then be written to

power-up the TP3420. Upon identifying the INFO 1 signal,

the device will set Status Indication type AP and pull INT low

to indicate that Activation is pending. No INFO 2 frames will

be transmitted until a Control instruction type AR is written to

the device, which allows the Activation sequence to proceed

as described above.

Once Activated, loss of frame alignment is assumed by the

TP3420A when a time which is equivalent to three frames

has passed without it detecting any of the valid pairs of line

code violations which obey the framing rule. If the NT does

detect alignment loss it will start to transmit INFO 2. At this

point the Error Indication (EI) primitive is set, the INT output

is pulled low and the receiver searches to identify the incom-

ing signal and attempt to re-acquire loop synchronization. If

it successfully re-establishes synchronization with the in-

coming signal (INFO 3 frames), a further interrupt is gener-

ated with Status Indication type AI and re-activation can be

completed by sending an AR command. If, however, the re-

ceiver subsequently identifies that the incoming line signal

has ceased, i.e. INFO 0 is being received, Status Indicator EI

is set and INT pulled low, with the transmitted frames

changed to INFO 2. Deactivation can then be completed by

a DR command, following which Status Indication type DI is

set and the INT output pulled low to indicate De-activation.

If required, a PDN instruction may be written to the Control

put.

I.430 recommends 2 timers should be available in an NT. An

Activation Request to the TP3420A should be associated

with the start of an external Timer 1, if required. Timer 1

should be stopped when the AI interrupt is generated follow-

ing successful Activation. If Timer 1 expires before AI is gen-

erated, however, Control Instruction type DR should be writ-

ten to the device to force de-activation. Timer 2, which is

specified to prevent unintentional reactivation, is not required

since the TP3420A can uniquely recognise INFO 1 frames.

ACTIVATION/DEACTIVATION: TP3420A IN TE MODE

Activation initiated by the TE: to activate the loop with the

TP3420A at the TE end the device must first be powered-up

by a PUP command, followed (Note 3) by a Control Instruc-

tion type AR, which is the Activation Request to begin trans-

mission of INFO 1 frames after verifying that INFO 0 is being

received from the NT. INFO 1 is a continuous pattern of 0+,

0−, and 6 ‘1’s repeated. At this point the TE is running from

its local oscillator and is not receiving any sync information

from the NT. When the NT recognises this “wake-up” signal,

it begins to transmit INFO 2, synchronized to the network

clock (following activation of the “U” interface, if applicable).

This enables the phase-locked loop in the TE’s receiver to

correctly identify bit timing from the NT and to synchronize its

own transmission to that of the NT. On identifying INFO 2 for

3 consecutive frames, the TE changes its transmit data to

INFO 3 and awaits the return of INFO 4 from the NT. Identi-

fication of INFO 4 completes the Activation sequence, so

Status Indication type AI is set, and the INT output pulled

low.

Activation initiated from the NT: when Activation is initiated

by the NT, if the TP3420A in TE mode is powered down, it

will pull the LSD pin and INT low on receiving a line signal.

Either of these can be used to “wake-up” a microprocessor.

A PUP command is required to enable the device to

power-up, identify the received signal, and acquire bit and

frame synchronization. Once INFO 2 has been identified, the

TP3420A will pull INT low, with Status Indication type AP set,

to alert the microprocessor that Activation is pending. The

microprocessor must respond by writing Control Instruction

type AR in order for Activation to proceed. INFO 3 frames are

then transmitted. Finally, an AI Status Indication interrupt is

generated when the NT replies with INFO 4 frames.

As in NT mode, once Activated, loss of frame alignment is

assumed by the TP3420A when a time equivalent to three

frames has passed without it detecting any of the valid pairs

of line code violations which obey the framing rule. If the TE

does detect alignment loss it will cease transmitting immedi-

ately. At this point the Error Indication (EI) primitive is set in

the Status Register, the INT output is pulled low and the re-

ceiver searches to re-acquire loop synchronization if INFO 2

or INFO 4 frames are still being received. If synchronization

is re-established, a further interrupt is generated, with Status

Indication type AI. If, however, the receiver subsequently

identifies that the incoming line signal has ceased, i.e. INFO

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