RAD Data comm ASM-20 Specifikace stáhnout pdf (Strana 18)

ASM-20

Installation and Operation Manual Chapter 1. Introduction

6/4/99 13:10 Functional Description 1-5

Modulation

Timing

This circuit supplies the transmit clock to the encoder. Three clock sources

are available:

• Internal oscillator

• External from the DTE

• Loop clock derived from the receive signal.

Setting the XMT CLK jumper determines the timing option. See Setting

Internal Jumpers and Switches in Chapter 2 for more information.

XMT Level

(optional)

Two options are available for the XMT level (signal level): 0 and -6 dBm.

XMT level is controlled by the XMT LVL jumper. See Setting Internal Jumpers

and Switches in Chapter 2 for more information on the XMT LVL jumper.

An optional output filter to the line is available. This filter can be ordered in

compliance with British Telecom and other PTT requirements.

Receiver

The receiver comprises several circuits as shown in the block diagram

(see Figure 1-6):

• The RECEIVE FILTER removes all the out-band frequencies.

• The AUTOMATIC EQUALIZER comprises several equalizers which are

activated according to baud rate.

• The digital AGC automatically compensates for the attenuation of the line.

Remote Power

Failure (RPF)

The Remote Power Failure feature allows the user at a central location to

detect a power failure in a remote modem. The remote power failure feature

can only be configured when the ASM-20/SA standalone unit (remote)

operates opposite the rack-mounted card ASM-20/R (central). When a

power failure occurs, ASM-20/SA transmits a special tone which is detected

by ASM-20/R and causes the ERR/RPF LED to light up. A special push button

located on the front panel of ASM-20/R allows the user to reset the RPF LED.

The RPF jumper in the standalone unit enables or disables the feature. The

RPF feature should be disabled for multipoint applications.

V.54 Diagnostics

V.54 loops are activated either by manual front panel push buttons or via the

DTE interface. The push buttons and the DTE interface can be enabled or

disabled separately by the SWITCH EN, ALB DTE, RLB DTE jumpers

respectively. See Setting Internal Jumpers and Switches in Chapter 2, for

more information.

Async to Sync

Converter

ASM-20 has an internal asynchronous to synchronous converter and

synchronous to asynchronous converter (used for asynchronous data).

A synchronous transmission is provided by internal conversion from

asynchronous to synchronous mode in compliance with ITU V.22 bis. In this

standard, the modem compensates for frequency deviation between the

modem and the DTE by adjusting the length of the stop bit of the async

character. If the modem’s frequency is lower than the DTE, the local

converter deletes one stop bit in every four (25%) or eight (12.5%)

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