MT90220
clock and frame pulse are fixed and must conform to
the ST-BUS specification.
The MITEL ST-BUS has 32 channels numbered 0 to
31. Two different mapping schemes are selectable.
The spaced mapping scheme uses 3 of every 4
channels. The grouped scheme uses the first 24
channels. Refer to Table 8 for details of Spaced DS-1
mapping, Table 9 for Grouped DS1 mapping. All
unused channels are tri-state.
The RXCK and RXSYNC pins are always defined as
inputs and are generated by external circuitry.
4.2.1 Mode 2 and 6: ST-BUS Interface for T1
In PCM Mode 2 the TXCK and TXSYNC pins are
defined as Inputs and in PCM Mode 6, the TXCK and
TXSYNC are defined as outputs. The RXCK and
RXSYNC are always defined as input pins.
The MITEL ST-BUS clock value is 4.096 MHz. The
frame pulse is 8 kHz and should be as defined in
Figure 9 or Figure 10 (see MITEL Application Note
MSAN-126).
In T1 applications, a DS-1 frame is 193 bits long and
corresponds to 1 framing bit and 192 payload bits.
The 192 payload bits are divided as 24 channels or
time slots of 8 bits each.
In the PCM Mode 6, the TXCK and TXSYNC pins are
defined as outputs. The source for the TXCK is
selected using TX PCM Link Control register
number 2 and can be any of the eight RXCK or four
external REFCK clocks. As there is no PLL inside the
MT90220, the source frequency has to be a valid ST-
DS1 Time slots
-
1
1
2
2
3
3
-
4
5
5
6
6
7
-
7
9
8
9
-
1
0
1
1
1
2
Voice/Data Channels
(DSTi/o)
ST-BUS
0
x
4
x
8
x
1
0
1
1
1
2
x
1
3
1
4
1
5
DS1 Time slots
-
1
3
1
4
1
5
-
1
6
1
7
1
8
-
1
9
2
0
2
1
-
2
2
2
3
2
4
Voice/Data Channels
(DSTi/o)
ST-BUS
1
6
x
1
7
1
8
1
9
2
0
x
2
1
2
2
2
3
2
4
x
2
5
2
6
2
7
2
8
x
2
9
3
0
3
1
Table 8 - T1Channel Mapping Using 3 Channels Every 4 Channels
ST-BUS
Bit Cells
(DSTx0-7)
...
Chan. 31 bit 0
Bit Cell
Chan. 0 bit 7
Chan. 0 bit 0
Chan. 1 bit 7
Bit Cell
...
Serial Bit
Stream
Unused or
High Impedance
Unused or
High Impedance
...
...
...
...
TXSYNC0-7
RXSYNC0-7
TXCK 0-7
RXCK 0-7
...
...
...
ST-BUS
Bit Cells
at DSTx0-7
Chan. N-1 bit 0
Bit Cell
Chan. N bit 7
Chan. N bit 0
Chan. N+1 bit 7
Bit Cell
...
...
...
...
Serial Bit
Stream
Unused or
High Impedance
Unused or
High Impedance
...
...
...
TXSYNC0-7
RXSYNC0-7
TXCK 0-7
RXCK 0-7
NOTE: The value N is 0, 4, 8, 12, 16, 20, 24 or 28 and corresponds to the unused channels.
Figure 9 - PCM Mode 2 and 6: ST-BUS Interface for T1 (Spaced Mapping)
25
MITEL [ MITEL NETWORKS CORPORATION ]
