Black Box ME760A-R2, Руководство пользователя

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10
LDM-MR19.2
2. Introduction
The 19.2 kbps RS-232 Line Driver (LDM-MR19.2 for short) is a short-range
modem which operates at full- or half-duplex with synchronous or asynchronous
transmission over unconditioned telephone lines. With an extended range of up
to 34 miles (55 km), the LDM-MR19.2 operates at any of eight selectable data rates,
up to 19,200 bps.
By using conditioned differential diphase modulation (Eurocom Std. D1), the
LDM-MR19.2 provides immunity from background noise, eliminates normal line
distortion, and enables efficient transmission and reception of serial data over
twisted-pair cable.
The LDM-MR19.2 is coupled to the telephone line through isolation
transformers. The transformers and electronic circuitry protect against AC or DC
overvoltages. The protection circuitry allows operation even when DC is connected
to the line, because of the following features:
• Transmit Level and Transmit and Receive Impedances are independently
selectable.
• Transmit timing is provided internally, derived externally from the
data terminal, or regenerated from the Receive signal.
• Receive timing is regenerated from the Receive signal.
Line communication is always synchronous. When you set the LDM-MR19.2 to
asynchronous mode, it performs an async-to-sync conversion in compliance with
the CCITT V.22 bis standard.
The LDM-MR19.2 also features V.54 diagnostic capabilities for performing local
analog loopback and local and remote digital loopback. In the digital loopback
mode, the operator at either end of the line may test both of the modems and
the line. The operator can control the loopback with either the front-panel
pushbuttons or Pins 18 and 21 of the V.24/RS-232 interface.