MT90812
Advance Information
multiplexed bus specifications. The MT90812 can operate in either
Α-Law
or
µ−Law
as defined in Control
register as specified in section “Control Register (CTL)” on page 54.
2.0
Local TDM Streams
There are two local serial Time Division Multiplexed (TDM) streams. These streams at STi/o0 and STi/o1
provide a link between the MT90812 and other peripheral devices, including those in the ST-BUS family (e.g.
MT9160B, MT9171/72, MT8930, MT8910). The two serial streams operate at 2.048 Mbit/s and are arranged in
125us wide frames, each comprising 32 8-bit channels. Refer to Section 9.2, “Serial Data Interface Timing”.
The MT90812 can support Primary Rate or Basic Rate devices. Using the Basic Rate devices (e.g. MT9171/72
DNIC) in dual port mode the D-Channel should be assigned to STi/o1 streams. D-channel signalling support is
provided for any timeslot on the STi/o1 streams for the HDLC Controller mode. The DBRT can access any
timeslot and stream. Refer to “D-Channel Signalling Support” on page 30 and “Local TDM Channel
Assignment” on page 76.
3.0
Expansion Bus
The expansion bus operates in 2 modes, IDX Link and TDM Link modes. The modes will be described in the
following sections. Section 24.1 describes the timing references used for both Expansion bus modes.
3.1
TDM Link Mode
In this mode, the expansion bus at EST0 and EST1, are regular output and input serial streams, respectively.
They operate at either 2.048, 4.096 or 8.192 Mbit/s. Refer to Fig. 4.
frame n
F0i
channel
STi/o1
i
A1
A2
i+32
...
E6
E7
E8
EST0/1
E1
E2
E3
E4
E5
...
E128
Figure 4 - Expansion Bus (TDM Link mode)
At 2.048Mb/s, the first block of 32 locations of Data Memory reserved for the expansion bus are used. The 32
incoming channels on EST1 are placed in expansion block 1 of Data Memory. At 4.096 Mb/s the 64 bytes are
utilized in expansion block 1 and 2. At 8.192Mb/s all 128 locations of Data Memory reserved for the expansion
bus are used. Refer to the description of the memory allocation in Section 5, “Address Memory Map”.
This mode allows linking larger matrices of MT90812 devices together. For example, at 2.048 Mb/s, eight
MT90812 devices can be connected together via a MT8980D (DX) switch, as shown in Fig. 5.
TRUNKS
AND PORTS
TRUNK S
AND PORTS
STi/o0-1
IDXa
STi/o0-1
IDXb
EST0
EST1
uport
EST0
EST1
uport
DX
uport
TRUNKS
AND PORTS
STi/o0-1
IDXh
EST0
EST1
uport
MPU
Figure 5 - Eight IDX Configuration using Expansion Bus TDM Link mode
8
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