MT9125AE 데이터 시트보기 (PDF) - Zarlink Semiconductor Inc

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MT9125AE

Dual ADPCM Transcoder

Zarlink Semiconductor Inc 

MT9125

F0i

DSTi/o

Channel 0

B1

Channel 1

B2

Preliminary Information

Channel 2

B1

Channel 3

B2

EN1

EN2

ADPCMi/o

B1

B2

ENS=0

EN1

EN2

ENS=1

ADPCMi/o

B1

B2

In ST-BUS mode the ENA, ENB1 and ENB2 input strobes are ignored. All timing is

dervied internally from the F0i, MCLK and ENS inputs.

Figure 4 - ST-BUS Mode Relative Timing

the device and must, therefore, be present whenever

a transcoding operation is required. These inputs

may be tied together and connected to the same

strobe for single channel operation. Only the B1

nibble is valid in this mode. Data is latched into the

DSTi pin with the falling edge of the bit clock while

output data is made available at DSTo on the rising

edge of the bit clock.

ST-BUS Conversion (F0i, C2o, EN1, EN2, ENS)

A simple converter circuit is incorporated which

allows ST-BUS signals to be converted to SSI

signals. In this manner it is very simple for an ST-

BUS application to be mixed with CODECs utilizing a

strobed data I/O.

This converter circuit consists of the F0i input and

C2o, EN1 and EN2 output pins (as well as the MCLK

input master clock). The output C4b clock and frame

pulse strobe (F0b), from the ST-BUS layer 1

transceiver, are connected directly to the master

clock (MCLK) and frame pulse (F0i) inputs of the

transcoder. A 2.048 MHz (C2o) bit clock output is

made available when a valid Frame Pulse is

connected to the F0i pin or the F0i pin is tied high. If

the F0i pin is tied low the C2o output is forced

continuously to a logic low level (not tri-stated).

Forcing the C2o output to logic low enhances power

conservation as well as removing a non-required

clock signal from the circuit. This 2.048 MHz bit clock

may be used to control external CODEC functions.

The 4.096 MHz and frame pulse signals are also

decoded into two output strobes corresponding to

the B1 and B2 channel timeslots of the ST-BUS.

These strobes (EN1 and EN2) are then used to

control the timing inputs of an external CODEC. A

typical example of this connection scheme is shown

in the application diagram of Figure 7.

The Enable Strobe pin (ENS) is used to position the

output strobes EN1 and EN2 within the ST-BUS

frame. Referring to Figure 4, when ENS=0 the output

strobes are positioned in channels 0 and 1 of the ST-

BUS frame. When ENS=1 the output strobes are

positioned in channels 2 and 3 of the ST-BUS frame.

This flexibility allows the transcoder to be used in ST-

BUS basic rate applications where channels 0 and 1

are defined as the D and C channels, respectively,

and also in line-card applications where the full

2.048 MHz bandwidth is used for conveying data

and/or digitally encoded voice information.

8-78

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