RAD Data comm ASM-10/8 ,

Chapter 1. Introduction ASM-10/8

Installation and Operation Manual

1-6 Functional Description 09/10/00 16:26

General This section contains functional descriptions of the circuit blocks of

ASM-10/8, primarily those circuits which are required for setting the desired

modem configuration (see Figure 1-6).

Encoder The encoder modulates the input data from the DTE using the conditional

diphase modulation technique.

The encoder can be configured to operate in one of the following different

modes:

• 4-wire full duplex

• 4-wire half duplex

• 2-wire half duplex

• 4-wire multipoint

• 2-wire multipoint.

This circuit supplies the transmit clock signal to the encoder.

The following clock sources are available:

• INT.CK (internal clock) – from the modem's internal crystal oscillator)

• EXT.CK (external clock) – from DTE, pin 24

• RCV.CK (receive clock) – recovered from the received signal

• ASYNC – asynchronous timing for working with the async to sync

converter in asynchronous applications.

Timing options are selected using the XMT TIMING jumpers.

ASM-10/8 has an internal asynchronous to synchronous converter (used for

asynchronous data).

Asynchronous 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 higher than the DTE, the local

converter extends the stop bit. 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%) characters. The remote converter will add a shorter stop bit (shorter

by 12.5% or 25%) before sending the data to the remote DTE.

Shortening the stop bits by 12.5% is suitable for frequency deviations up to

1.1% and shortening the stop bits by 25% is suitable for frequency

deviations up to 2.3%.

Four options are available for the XMT level (signal level): 0, -3, -6, -9 dBm.

An optional output filter for the line is available. This filter complies with

Bell 43401 standard and meets British Telecom requirements.