4-192

MH89790B

Preliminary Information

Figure 6 - ST-BUS Stream Format

CHANNEL

31

030

BIT

CHANNEL

CHANNEL

CHANNEL

CHANNEL

31

0

BIT

BIT

BIT

BIT

BIT

BIT

BIT

• • •

Least

Significant

Bit (Last)

Most

Significant

Bit (First)

(8/2.048)

µs

125

µs

76

5

4

3

2

1

0

Data Input (DSTi)

The MH89790B receives information channels on

the DSTi pin. Of the 32 available channels on this

serial input, 30 are defined as information channels.

They are channels 1-15 and 17-31. These 30

timeslots are the 30 telephone channels of the CEPT

format numbered 1-15 and 16-30.

Timeslot

0

and

16

are

unused

to

allow

the

synchronization and signalling information to be

inserted, from the Control Streams (CSTi0 and

CSTi1). The relationship between the input and

output ST-BUS

stream and

the CEPT line is

illustrated in Figures 7 to 11.

In common channel

signalling mode timeslot 16 becomes an active

channel.

In this mode channel 16 on DSTi is

transmitted

on

timeslot

16

of

the

CEPT

link

unaltered. This mode is activated by bit 5 of channel

31 of CSTi0.

Control Input 0 (CSTi0)

All the necessary control and signalling information

is input through the two control streams. Control

ST-BUS input number 0 (CSTi0) contains the control

information that is associated with each information

channel. Each control channel contains the per

channel digital attenuation information, the individual

Table 2. Per Channel Control Word: Data Format for CSTi0 Channels 0-14, and 16-30

BIT

NAME

DESCRIPTION

7

DATA

Data Channel: If ‘1‘, then the controlled timeslot on the CEPT 2048 kbit/s link is treated as a

data channel; i.e., no ADI encoding or decoding is performed on transmission or reception,

and digital attenuation is disabled.

If ‘0‘, then the state of the ADI pin determines whether or

not ADI encoding and decoding is performed.

6

LOOP

Per-Channel Loopback: If ‘1‘, then the controlled timeslot on the transmitted CEPT 2048

kbit/s link is looped internally to replace the data on the corresponding received timeslot. If

‘0‘, then this function is disabled. This function only operates if frame synchronization is

received from the CEPT link. If more than one channel is looped per frame only the first one

will be active.

5,4,3

RXPAD4,2,1

Receive Attenuation Pad: Per timeslot receive attenuation control bits.

RXPAD4

0

0

0

0

1

1

1

1

RXPAD2

0

0

1

1

0

0

1

1

RXPAD1

0

1

0

1

0

1

0

1

Gain (dB)

0

-1

-2

-3

-4

-5

-6

1

2,1,0

TXPAD4,2,1

Transmit Attenuation Pad: Per timeslot transmit attenuation control bits.

TXPAD4

0

0

0

0

1

1

1

1

TXPAD2

0

0

1

1

0

0

1

1

TXPAD1

0

0

1

0

1

0

1

0

Gain (dB)

0

-1

-2

-3

-4

-5

-6

1