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MH89770N

T1/ESF Framer & Interface

Mitel Networks 

Preliminary Information

MH89770

Zero Code Suppression

The combination of bits 5 and 6 in Master Control

Word 1 allow one of three zero code suppression

schemes to be selected. The three choices are:

none, binary 8 zero suppression (B8ZS), or jammed

bit (bit 7 forced high). No zero code suppression

allows the device to interface with systems that have

already applied some form of zero code suppression

to the data input on DSTi. B8ZS zero code

suppression replaces all strings of 8 zeros with a

known bit pattern and a specific pattern of bipolar

violations. This bit pattern and violation pattern is

shown in Figure 4. The receiver monitors the

received bit pattern and the bipolar violation pattern

and replaces all matching strings with 8 zeros.

Loopback Modes

Remote and digital loopback modes are enabled by

bits 6 and 7 in Master Control Word 2. These modes

can be used for diagnostics in locating the source of

a fault condition. Remote loop around loops back

data received at RxR and RxT back out on OUTA

and OUTB, thus effectively sending the received

DS1 data back to the far end unaltered so that the

transmission line can be tested. The received signal

with the appropriate received channels on the DS1

side made available in the proper format at DSTo.

The digital loop around mode diverts the data

received at DSTi back out the DSTo pin. Data

received on DSTi is, however, still transmitted out via

OUTA and OUTB. This loop back mode can be used

to test the near end interface equipment when there

is no transmission line or when there is a suspected

failure of the line.

The all ones transmit alarm (also known as the blue

alarm or the keep alive signal) can be activated in

conjunction with the digital loop around so that the

transmission line sends an all 1's signal while the

normal data is looped back locally.

The MH89770 also has a per channel loopback

mode. See Table 6 and the following section for more

information.

Per Channel Control Features

In addition to the two master control words in CSTi0

there are also 24 Per Channel Control Words. These

control words only affect individual DS0 channels.

The correspondence between the channels on

CSTi0 and the affected DS0 channel is shown in

Fig. 3. Each control word has three bits that enable

robbed bit signalling, DS0 channel loopback and

inversion of the DS0 channel. A full description of

each of the bits is provided in Table 6.

Transmit Signalling Bits

Control ST-BUS input number 1 (CSTi1) contains 24

additional per channel control words. These 24

ST-BUS channels contain the A, B, C and D

signalling bits that the device uses at transmit time.

The position of these 24 per channel control words in

the ST-BUS is shown in Figure 3 and the position of

the ABCD signalling bits is shown in Table 7. Even

though the device only inserts the signalling

Bit

Name

Description

7-3

IC

Internal Connections. Must be kept at 0 for normal operation.

2

Polarity When set, the applicable channel is not inverted on the transmit or the receive side of

the device. When clear, all the bits within the applicable channel are inverted both on

transmit and receive side.

1

Loop

Per Channel Loopback. When set, the received DS0 channel is replaced with the

transmitted DS0 channel. Only one DS0 channel may be looped back in this manner at

a time. The transmitted DS0 channel remains unaffected. When clear the transmit and

receive DS0 sections operate normally.

0

Data

Data Channel Enable. When set, robbed bit signalling for the applicable channel is

disabled. When clear, every 6th DS1 frame is available for robbed bit signalling. This

feature is enabled only if bit 1 in Master Control Word is low.

Table 6. Per Channel Control Word 1 Input at CSTi0

Bit

Name

Description

7-4

Unused Keep at 0 for normal operation

3

A

These are the 4 signalling bits inserted in the appropriate channels of the DS1 stream

2

B

being output from the chip, when in ESF mode. In D3/D4 modes where there are only

1-0

C, D

two signalling bits, the values of C and D are ignored.

Table 7. Per Channel Control Word 2 Input at CSTi1

4-133

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