Toshiba Strata AirLink Installation Manual page 73

The E1 devices receive each processed (but not formatted) 31 B + D frame from the CPU and
transmits it (after formatting) to its Base Station through its TX line transformer. The same is true
from the receiving side. The CPU performs the protocol conversion. Both TX and RX transfers are
actuated in DMA mode by the CPU.
The E1 device connects to the matrix using four internal 2048 kbs synchronous PCM buses with
the following signals:
o RD01 internal PCM channel n1 received data (U7)
o XDI1 internal PCM channel n1 transmit data (U7)
RD02 internal PCM channel n2 received data (U13)
o
o XDI2 internal PCM channel n2 transmit data (U13)
o RD03 internal PCM channel n3 received data (U25)
o XDI3 internal PCM channel n3 transmit data (U25)
RD04 internal PCM channel n4 received data (U35)
o
o XDI4 internal PCM channel n4 transmit data (U35)
The four internal 2048 kbs synchronous PCM busses transfer the data between each E1 device and
the matrix. The matrix places the data on the backplane PCM channels.
Protectors
The RX and TX transformers connect to the E1 line through protector devices. Current-limiting
resistors are used on both sides of the transformers. Tranazorb U45~U47, U53, U57~U58, and
U62~U63 and Gas Tubes G1~G8 devices provide fast protection from lightning by sending
sudden surges to the frame around the RWIU PCB.
Additional protection is provided by the secondary line transformers by dual MMBT7000 diodes.
All the line transformers RX and TX are breakdown-rated at 1500 Vrms. Loop back controls and
Base Station resets are provided for each Base Station by a relay. Each relay is controlled by the
CPU using an output port signal. Transistors drive each relay.
Power (-40VDC) transfers from each Base Station to the associated remote Base Station are
performed using a standard phantom interface on the central taps of the secondary of each TX and
RX transformer of the E1 interface. An electronic circuit breaker with associated power Field
Effect Transistor (FET) is used for each Base Station E1 interface.
In the case of a short circuit on the -40VDC side of one the phantom interfaces, the
Important!
electronic breaker turns off its associated power FET. After about five seconds, it
tries to verify that the short is gone by turning on the power FET for a shorter
period (about 200 ms). If the short is gone, the circuit breaker turns on its power
FET permanently. If the short is still present, it continues to retry the circuit.
The same device protects the PCB against a rush current at Base Station power up. Each electronic
circuit breaker block is turned on/off by the CPU using the output port that drives the LED of a
photocoupler. A short circuit indication flag is provided to the CPU for each electronic circuit
breaker. The following are additional protection devices for each E1 interface:
o Four slow-blow fuses
o One polyswitch
Strata AirLink Installation Guide 5/00
RWIU System Installation
RWIU Additional Information
63