Preliminary Information
MH89790B
System Side
Line Side
•
•
COM1
O
A
O
F1
F2
O
O
75Ω
O
O
•
120Ω
B
O
Through Hole
Units
Parameter
(Units)
TFS 2915
TFS 2574-4
-4
-5
Transformer Type
Inductance (mH)
input
output
output
(COM1-75Ω)
(COM1-120Ω)
>1.2
>1.9
0.49
0.81
>1
>1.5
Turns Ratio
(COM1-75Ω):(A-F1):(B-F2)
(COM1-120Ω):(COM1-75Ω)
1:1:1
1•26:1
0•4:1:1
1•28:1
1•12:1:1
1•22:1
Line Impedance (Ω)
75/120
-
75/120
+12
75/120
+5
Operational Voltage (Volts)
Dielectric Strength (Vrms)
1500
1500
1500
Table 18. Typical Parameters of the Input and Output Transformers
Applications
SIGNALLING - Signalling information on the ISDN
primary rate interface is carried over the D-channel
using LAPD procedures. The ISDN D-channel is
created by placing the MH89790B in Common
Channel Signalling mode. The D-channel is tapped
off from the ST-BUS and connected to the MT8952
Protocoller Controller. It receives and transmits data
packets serially, in accordance with LAPD protocol
requirements.
ISDN Primary Rate User Network Interface
Typical examples of primary rate interfaces are high
capacity links from a PBX to a Central Office
Exchange or multiple links between PBX’s in a large
private network. With the advent of Integrated
Services Digital Networks (ISDN) a limited set of
network interfaces is specified to allow equipment
from different vendors to operate in the network.
The MH89790B conforms to the ISDN S/T Primary
Rate reference point standard, which calls for 30 B
channels (64 kbit/s) and one D channel (64 kbit/s).
Figure 15 illustrates a typical application of the
MH89790B in an ISDN environment.
CONTROL
-
The MT8920B (STPA) provides
microprocessor access to directly control the
MH89790B through its transmit and receive dual port
RAMs. Status information can generate interrupts to
notify the system in case of slips, loss of
synchronization, alarms, violations, etc.
Interfacing to the Coaxial Cable Transmission
Line
Three types of information are passed through serial
busses of the MH89790B:
Reliable operation of the CEPT link is directly related
to the type of transmission medium and method of
interfacing. Coaxial cables provide excellent
transmission mediums if used properly. One of the
most important things to remember is that the
receive end of the cable must not be connected to
ground, as shown in Figure 16. If both ends are
USER DATA - The data streams of the MH89790B
are shown connected to the MT8980 Digital
Crosspoint Switch. This allows voice and data
channels to be switched dynamically within the
system.
4-205
MITEL [ MITEL NETWORKS CORPORATION ]
