6/4/99 13:10 Overview 1-1
Chapter 1Introduction

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 miles) 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 configurations:
• Point-to-point applications (see Figure 1-1)
• Modem link application (see Figure 1-2)
• Tail-end for digital networks application (see Figure 1-3).
HOST
ASM-20 ASM-20
4-WIRE
Up to 2 3 k m
19.2 - 256 kbs
RAD RAD
DTE
Term ina l
Figure 1-1 Point-to-point Application