Atari 835 Quick start guide

835 DIRECT
CONNECT MODEM
FIELD SERVICE
MANUAL
A.
ATARI
QAWwwCommunications Company
FD100268
Rev. 01
March* 1983

COPYRIGHT© 1983 BY ATARI, INC. ALL RIGHTS RESERVED.
No part of this publication may be reproduced by any mechanical, photographic, or
electronic process, or in the form of aphonographic recording, nor may it be stored in
aretrieval system, transmitted, or otherwise copied for public or private use, without
permission from the publisher.
Published By:
ATARI, INC.
1265 Borregas Avenue
P.O. Box 427
Sunnyvale, California 94086
r\
835 Direct Connect Modem
Field Service Manual

TM
835 DIRECT CONNECT MODEM
FIELD SERVICE MANUAL

Atari believes that the information described in this manual is accurate and reliable,
and much care has been taken in its preparation. However, no responsibility, financial
or otherwise, shall be accepted for any consequences arising out of the use of this
material. Information contained herein is subject to change. Revisions may be issued
to advise of such changes and/or additions.
Correspondence regarding this document should be forwarded to Director of Technical
Support, Consumer Product Service, Atari Incorporated, 845West Maude Avenue,
Sunnyvale, CA 94086.
835 Direct Connect Modem
Field Service Manual

TABLE OF CONTENTS
Section Title Page
INTRODUCTION V
1THEORY OF OPERATION 1-1
Introduction 1-1
Overview 1-1
Serial I/O Interface 1-2
835 Controller Chip 1-2
Functions of the Controller Chip 1-2
On Hook/Off Hook 1-2
Dial Digit 1-2
Originate/Answer Mode 1-2
Send Data 1-3
Receive Data 1-3
Present Status 1-3
Analog Loopback 1-3
Audio Off/On 1-3
Other Functions 1-3
Modem Chip 1-4
Transmit 1-4
Receive 1-4
Analog Loopback 1-4
Line Interface 1-5
Power Supply 1-5
2SILKSCREEN AND SCHEMATICS 2-1
3TEST PROCEDURES 3-1
Equipment Required 3-1
Power-Up Sequence 3-1
Test Sequence 3-1
4DIAGNOSTIC FLOWCHART 4-1
5PARTS LIST 5-1
6SERVICE BULLETINS 6-1
iii
835 Direct Connect Modem
Field Service Manual

LIST OF ILLUSTRATIONS
Section
1
Title
835 Direct Connect Modem Block Diagram
1
835 Direct Connect Modem
Field Service Manual IV

INTRODUCTION
The ATARI 835™ Direct Connect Modem Field Service Manual is organized in six
sections:
•THEORY OF OPERATION -Overview of how the electrical theory of the
modem operates.
•SILKSCREEN AND SCHEMATIC -Electrical drawings of the printed
circuit board and layout.
•TESTING AND TROUBLESHOOTING -Procedures for1testing the unit.
•835 FLOWCHART -Block diagram of the procedures for testing,
troubleshooting, and repairing adefective 835 unit.
•PARTS LIST -List of parts available from ATARI for repairing and
maintaining the 835 unit.
•SERVICE BULLETINS -Section to be used to hold service bulletins
released by the Director of Technical Support. These bulletins will include
changes in recommended repair procedures and required modifications for
units in the field.
IMPORTANT: In order to test the unit completely, the customer must return the
following items to the Service Center: 835 Direct Connect Modem, 835 power
adaptor, and Telelink n™ Cartridge.
835 Direct Connect Modem
Field Service Manual v

i

SECTION ONE
THEORY OF OPERATION
INTRODUCTION
The 835TM Direct Connect Modem (DCM) is designed for use with the Bell 103 Telephone
System. It operates at atransfer rate of 300 Baud. Features include, Automatic Pulse
Dialing, Software controlled Originate/Answer Mode Switching, and Audio Monitoring of the
telephone line. The 835 allows for transfer of data over the telephone line directly
(bypassing the telephone handset).
WARNING: Do not hook the 835 DCM to Bell Telephone's "Horizon®- System". Doing so
damages the telephone system. "Horizon" is a4-wire, non-standard
configuration that accepts only touch-tone pulsing.
OVERVIEW
The 835 DCM connects to the 400/800 Computer through the Serial I/O Bus and is
compatible with the 1200XL Computer. Aseparate 22 volt AC adaptor furnishes the power
for the 835 DCM. The two major ICs used in the 835 DCM are an 8048 microprocessor and
aTexas Instruments Modem IC.
The 835 DCM consists of the following functional units (see Figure 1-1):
•Serial I/O Interface
•835 Controller (8048)
•Texas Instruments Modem Chip (TI99532)
•Telephone Line Interface
•Power Supply
All components referenced in the following detailed description of the 835 DCM functional
units can be found on Page 1of the oversize drawing package included with this manual.
TELEPHONE
AC in
Figure 1-1. 835 Direct Connect Modem Block Diagram
835 Direct Connect Modem 1-1
Field Service Manual

SERIAL I/O INTERFACE
This circuit consists of the two 13-pin SIO Connectors (32 and 33) and the LM339
Comparator (M6).
•Pins 3, 9, and 13 are inputs to the computer straight from the 835 Controller (M5).
•Pins 2,5,7, and 10 are outputs from the computer. The signals coming in on these
pins go through the Comparator (M6), which acts as- alatch, before reaching the
835 Controller (M5).
835 CONTROLLER CHIP
The 835 Controller chip is an Intel 8048 Microprocessor with Atari-designed firmware. The
Controller performs the following functions:
•Translates the computer commands
•Sends data and status to the computer
•Receives data from the computer
•Sends data and commands to the Modem Chip
•Receives data and status from the Modem Chip
The 835 Controller (M5) communicates with the computer using the normal SIO Protocol at
arate of 300 Baud. It communicates with the Modem Chip using amodified RS-232C
Protocol at arate of 300 Baud.
FUNCTIONS OF THE CONTROLLER CHIP
On Hook/Off Hook
Upon receipt of either command from the computer, the Controller sends asignal out on Pin
24 causing the Relay (Kl) to change state. The signal connects (Off-Hook) or disconnects
(On-Hook) the 835 with the telephone line. The default condition is On-Hook.
Dial Digit
Upon receipt of this command from the computer, the Controller toggles the line Relay (Kl)
via Pin 24 to accomplish Pulse Dialing. The timing for this operation conforms to FCC and
TAP (Canadian) specifications.
Originate/Answer Mode
Upon receipt of this command from the computer, the Controller sets Pin 37 HIGH
(Originate) or LOW (Answer). This causes the Modem Chip (M4) to change to the correct
transmit and receive frequencies. The default condition is Originate.
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835 Direct Connect Modem
Field Service Manual 1-2