MH89770
Preliminary Information
The Asynchronous Communications Interface
Adapters (ACIA) provide a standard RS232 interface
that is compatible with many off-the-shelf modems
and data sets. A single microprocessor is capable of
handling the protocol conversion between the RS232
ports and the MT8952 HDLC protocol controller.
The MH89770 and the MT8941 form the T1
interface. The MH89770 converts the data received
on the ST-BUS into a 1.544 MHz T1 stream. All of
the formatting and decoding of the T1 signal is
performed by this device. The MT8941 provides the
clock synchronization required to operate in a loop
timed mode. Digital phase-locked loop #2 provides
ST-BUS clocks that are synchronized to the
extracted 8kHz, and digital phase-locked loop #1
provides the transmit 1.544 MHz clock synchronized
to the ST-BUS.
The MT8952 interfaces directly to the ST-BUS, which
in turn interfaces directly to the T1 interface devices.
Instead of the MT8952 operating at 64 kbit/s
continuously, it operates at 2.048 Mbit/s and
inputs/outputs an 8 bit burst every 125 µsec. This
feature eliminates the need for an additional rate
conversion circuit to multiplex the HDLC outputs up
to the T1 data rate. Each of the HDLC chips is
assigned a timeslot on the ST-BUS in a manner that
is similar to enabling a voice codec. When the
MT8952 is not enabled the output driver is tristated.
7. High Speed Data Transmission Link
High speed data links are becoming increasingly
popular in private networks and computer
communications. The basic mode of transmission is
to assemble data into packets (e.g., HDLC or
ethernet) which are transported on a T1 link
configured as a 1.536 Mbit/s serial channel. No T1
repeaters are required if the transmission link length
is 1300 ft. or less (e.g., business complex or
university). However, if the transmission link length is
greater than 1300 ft., a repeatered T1 line must be
leased from the local telephone operating company.
The channel assignment circuit is therefore very
simple. The switch matrix, in the message mode,
passes monitor and control information between the
microprocessor and the T1 interface over ST-BUS
stream 0. The MT8980 is also used to reformat the
ST-BUS data streams between the protocol
converter and the MH89770 interface.
Protocol Converter
Switch Matrix
T1 Interface
MH89770
MT8952
MT8980
CDSTo
CDSTi
TxCEN
DSTi
OUTA
STi0
STo0
STo1
STi1
EQUAL-
IZER
DSTo
OUTB
RxT
STo2
STi2
CSTi1
CSTo
RxCEN
•
STo3
CSTi0
RxR
C2i
F0i
C4i
F0i
F0i
C4i
E8Ko
C1.5i
MT8941
DPLL #1
CVb
F0i
C1.5i
12.352
MHz Osc.
C12i
MICRO
DPLL #2
F0b
F0i
•
C8Kb
C16i
C4b
C20
C4i
C2i
16.384
MHz Osc.
Figure 17 - High Speed Data Transmission Link
4-148
MITEL [ MITEL NETWORKS CORPORATION ]
