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

Send Data
Upon receipt of this command from the computer, followed by asingle, asynchronous
character on Pins 27 and 39, the Controller sends the same single asynchronous character to
the Modem Chip (M4) on Pin 38.
Receive Data
Upon receipt of this command, the Controller sends asingle character to the Computer on
Pin 21, if acharacter is available. The Controller receives characters from the Modem Chip
(M4) on Pins 1and 34.
Present Status
Upon receipt of this command, the Controller sends Status information to the computer on
Pin 21.
Analog Loopback
Upon receipt of this command, the Controller sets the Modem Chip (M4) to the Analog
Loopback mode by pulling Pin 23 HIGH. This, in effect, disconnects the telephone line from
the Modem Chip (M4), allowing the Modem Chip (M4) to be tested for correct functioning.
Audio Off/On
Upon receipt of this command, the Controller sends asignal out Pin 35, controlling Audio
Monitoring of the telephone line.
I
Other Functions
•Setting the Baud Rate of the Modem Chip (M4) to 300 Baud on Pin 36
•Monitoring the Carrier Detect line from the Modem Chip (M4) on Pin 33
•Turning the Carrier Detect LED on with Pin 22 when Pin 33 goes Low
•Running atest on itself and the Modem Chip at power-up
835 Direct Connect Modem
Field Service Manual 1-3

MODEM CHIP
The Modem Chip is aTexas Instruments 99532 IC which uses Frequency Shift Keying to
transmit and receive serial binary data over the telephone line.
The Modem Chip takes the digital signals from the S35 Controller (M5) and converts them to
Analog signals for the telephone line and vice versa. In addition, the Modem Chip detects the
presence of acarrier wave on the telephone line and passes this information on to the 835
Controller (M5).
Transmit
•300 Baud character formatted data is placed on Pin 10 by the 835 Controller (M5).
•ALOW on Pin 13 sets the Transmitter for Bell 103 type output.
•Pin 12 receives aHIGH (Originate) or LOW (Answer) signal from the 835 Controller
(M5) to set the Transmit and Receive frequencies.
-In the Originate mode the transmitter issues asinewave tone on Pin 16 at 1270Hz
when Pin 10 is HIGH, and a1070Hz tone when Pin 10 is LOW.
-In the Answer mode the transmitter issues asinewave tone of 2225Hz on Pin 16
when Pin 10 is HIGH, and aTone of 2025Hz when Pin 10 is LOW.
Receive
When the Modem Chip detects aCarrier signal on Pin 15, it pulls Pin 2LOW. This alerts the
835 Controller (M5) that aCarrier has been detected. Pin 2stays LOW until Disconnect
occurs.
•Turn-On and Turn-Off timing of the Carrier Detect is provided by the circuit
connected to Pin 3of the Modem Chip.
•In the Originate mode, when Pin 15 of the Modem Chip receives a2025Hz, sinewave
tone, Pin 4goes LOW. A2225Hz, sinewave tone sets Pin 4HIGH.
•In the Answer mode a1070Hz signal on Pin 15 sets Pin 4LOW, and a1270Hz, signal
sets Pin 4HIGH.
Analog Loopback
AHIGH on Pin 1of the Modem Chip effectively disconnects it from the Line Interface. In
addition it connects the transmitter and receiver portions of the chip together, allowing
transmitted data to be "looped back" to the computer. This "loop back" tests the internal
analog and digital circuits of the Modem Chip.
835 Direct Connect Modem
Field Service Manual 1-4

LINE INTERFACE
Adescription of the Line Interface functions follows.
•OFF/ON HOOK signals and PULSE DIALING signals are sent from Pin 24 of the
835 Controller (M5) through the Multiplexor (M3) to the Relay (Kl).
•TRANSMIT signals are sent from Pin 16 of the Modem Chip (M4) to Pin 2fthe Op-
Amp (M2) for amplification. Then from Pin 1of (M2) to the Transformer (Tl) and
on to the telephone line, if Relay (Kl) is closed.
•RECEIVE signals come from the telephone line across the Transformer (Tl) and
into Pin 5of Op-Amp (M2). In M2 they are separated from the local Transmit
signals and sent on to Pin 15 of the Modem Chip (M4). These Receive signals are
also applied to Pin 2of the Multiplexor (M3).
•When the 835 Controller (M5) sends asignal out Pin 35 to Pin 10 of the Multiplexor
(M3), the Audio signals from the telephone line (e.g., dialtone, or someone talking)
are sent to the computer. They are heard on the TV Speaker.
POWER SUPPLY
The Power Supply receives 22 VAC from the external Power Adaptor and converts it to the
following DC voltages.
•+V (=18v) Used for the Hook Relay and Carrier LED Drive Circuits
•+12V Used by the Modem Chip (M4)
•+5V Used throughout the PC Board
•-5V Used for the Hook Relay Drive Circuit and the Modem Chip (M4)
835 Direct Connect Modem
Field Service Manual 1-5

SECTION TWO
SILKSCREEN AND SCHEMATIC
An oversized silkscreen and schematic are stapled to the front cover of the
manual.
835 Direct Connect Modem
Field Service Manual 2-1

SECTION THREE
TEST PROCEDURES
IMPORTANT: In order to test the unit completely, the customer must return the 835 DCM,
the 835 power adaptor, and the Telelink II Cartridge to the service center.
EQUIPMENT REQUIRED
•Standard Tool Kit
•Oscilloscope
•Chip Remover
•ATARI 800TM Computer
•ATARI 835 Test Diskette
•ATARI 810TM Disk Drive
•BASIC Cartridge
•Digital Voltmeter (optioned)
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 teat accepts only touch-tone pulsing.
POWER-UP SEQUENCE
Power up the 810 Disk Drive and insert the test diskette.
Insert the BASIC cartridge in the computer. Leave the computer off.
Connect the 835 DCM and power it up. The Power LED should light and stay lit. The On-
Line LED should flash once and stay off. The Relay (Kl) should click once. If this series of
events does not occur, go to the Troubleshooting Flowchart, Section 4, page 4-2.
Turn on the computer to boot the test diskette. This automatically loads the device handler
required for the 835 DCM.
TEST SEQUENCE
When READY appears on the screen, type RUN"D1:TEST835" and press RETURN. This
loads and runs the program used for testing the 835 DCM.
When the title appears on the screen, type any key on the computer and the Option Menu
appears.
The following procedure tests all functions of the 835 DCM. If you prefer to follow these
procedures in flowchart format, turn to the page referenced at the start of each sequence.
If afunction does not operate properly, you must turn to the flowchart to locate the repair
procedures.
835 Direct Connect Modem
Field Service Manual 3-1

Operation
TOGGLE TV SOUND ON TEST
Press key 2.
Explanation
Flowchart Entry Page 4-6.
This key toggles the TV sound ON.
Press key 1. This key toggles the direction to ANSWER. You
should hear ahigh-pitched tone coming from the
TV speaker.
Press key 1,again.
Press key 2.
This toggles the direction to Originate. You
should hear alow-pitched tone.
This toggles the TV sound OFF.
TELEPHONE OFF-HOOK TEST Flowchart Entry, Page 4-5.
Press key 3. This key toggles the telephone OFF-HOOK. You
should hear the Relay click. The right-hand
column of the Option Menu read: OFF.
Press key 3, again. This toggles the telephone ON-HOOK. You
should hear the Relay click. The right-hand
column of the Option Menu reads: ON.
Press key 9. This key toggles the telephone OFF-HOOK (the
Relay clicks on) and sets the Carrier Detect
circuit in operation. AWAITING FOR CARRIER
MESSAGE appears on the screen. It should
remain for 30 seconds, at which time the Relay
should click off and the Option Menu should
return to the screen.
AUTODIAL TEST Flowchart Entry, page 4-8.
Press key 7. When you press key 7, awarning message about
"Horizon" phone systems appears, along with a
request for the local telephone number of TIME.
If the modem is not hooked up to atelephone
line, ignore this request and press RETURN.
Key 7tests the Autodial function of the 835. A
menu entitled AUTODIAL OPTION appears on
the screen with three options. Option #1 is for
testing the modem without being connected to a
telephone line. Options #2 and #3 can also be
used for testing the 835, but only if you have a
telephone line connected to it.
835 Direct Connect Modem
Field Service Manual 3-2

Operation Explanation
If you Press key 1, the Relay should click on.
After athree second wait (waiting for Dialtone),
the Relay starts pulsing as the digits are dialed.
The Relay starts with short pulses for the one
and then sends pulses progressively longer, with
0being the longest. After 30 seconds (waiting
for carrier), the Menu returns to the screen.
Flowchart entry, page 4-13.
This key starts the Analog Loopback Test, which
tests the internal circuitry of the Modem IC
(M4). The following sequence of events should
occur:
•The screen turns gray and displays CARRIER
(ACQUIRED).
•The On-Line LED on the 835 lights up.
•The data sent from the computer to the 835
and the data sent from the 835 to the
computer displays on the screen. This data
should be identical.
The above procedure completes the testing of the 835 DCM.
Be sure the Telelink II™ cartridge works correctly, according to the Operator's Manual. If
not, replace it. Be sure the customer uses Telelink II exactly as the Operator's Manual
instructs.
ANALOG LOOPBACK TEST
Press key 8.
835 Direct Connect Modem
Field Service Manual 3-3

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