
MT90503
Data Sheet
40
Zarlink Semiconductor Inc.
4.2 TDM Module
The general architecture of the TDM bus consists of three main elements.
The TDM bus interface which is coupled directly to the bus pins and manages the timing requirements of the
H.100/H.110 interface.
The datapath management for transporting the bytes from the TDM bus to the circular buffers (located in the
external data memory).
The TDM clocking mechanism, this enables the MT90503 to be H.100/H.110 bus master capable and
communicates with the clock recovery module.
4.2.1 TDM Bus Interface
The MT90503 TDM Module interfaces with all 32 data streams of the H.100/H.110 bus. The maximum data rate of
8.192 Mbps determines the total bus capacity of 4096 TDM TSST. The MT90503 can process up to: 2048
transmitting TDM TSST and 2048 receiving TDM TSST within one frame of 125
μ
s.
One less TDM channel is carried for each CAS channel that is desired. If all TDM channels have CAS, then 1024
transmit and 1024 receive channels is the limit. The MT90503 can drive out data on any particular TSST (Time
Slot/Stream), or read in data from any particular TSST.
Each individual time slot or DS
0
on the H.1x0 bus is assigned by a unique TSST number, based on the following
equation:
The timeslot ranges from 0 to 31 for 2MHz streams, from 0 to 63 for 4MHz streams, or from 0 to 127 for 8MHz
streams.
The 16 lowest data streams are capable of running at a data rate lower than 8.192 MHz. The streams are grouped
in fours and each quartet must run at the same data rate. Streams [3:0], [7:4], [11:8] and [15:12] can each run at
2.048, 4.096 or 8.192 MHz as a group. This allows backward compatibility with older, slower TDM buses. In the
reduced rate, the data is still latched using the CT_C8_A or _B clock-edge, but using every second or every fourth
clock-edge. The streams numbered [31:16] must always run at 8.192 MHz.
The TDM bus can also be configured to use only 4, 8, or 16 streams. This configuration requires less processing of
TDM bytes and, also allows a reduced mclk speed. The 4-stream mode is useful for conducting tests, while the
16-stream mode allows mclk speed to be cut in half while still allowing half the bandwidth of a full H.100/H.110 bus.
When the H.100/H.110 bus is carrying CAS signalling bits, every even stream carries regular TDM data bytes, and
is associated with an odd stream that carries CAS bits and the indication of the beginning of the multiframe. For
TSSTs that are input to the MT90503, the multiframing is provided by the framer. For TSSTs that are generated by
the MT90503, the output multiframing is provided by the MT90503; there is one multiframe which is common to all
the T1 channel signals and one multiframe which is common to all the E1 channel signals. On the input, the
multiframing is independent for each TSST and the MT90503 synchronises all of them to its multiframe.
TSST =
timeslot * 32 + stream
(timeslot * 2+1) * 32 + stream
(timeslot * 4+3) * 32 + stream
for 8MHz streams
for 4MHz streams
for 2MHz streams