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Overview 1-1
Chapter 1
Introduction
1.1 Overview
The ASM-20 short range modem operates synchronously or asynchronously at
full-or half-duplex, over unconditioned lines. ASM-20 has a range of up to 23 km
(14 mi) and operates at selectable data rates from 19.2 kbps to 256 kbps.
ASM-20 uses conditioned diphase modulation (EUROCOM Std. D1) to provide
immunity from background noise, eliminate normal line distortion, and enable
efficient transmission and reception of serial data over a twisted pair cable.
Transmit timing is provided internally, or derived externally from the data terminal
or regenerated from the receive signal.
Receive timing is regenerated from the data.
Applications
The following diagrams illustrate ASM-20 in a variety of applications:
• Point-to-point
• Modem link
• Tail-end for digital networks.
HOST
ASM-20 ASM-20
4-WIRE
Up to 23 km
19.2 - 256 kbs
RAD RAD
DTE
Termina l
Figure 1-1. Point-to-point Application