Hayes Microcomputer Products Stack Smartmodem User manual

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Smartmodem
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AA CO OH RD SD TR MR
Owner’s Manual

HAYES STACK SMARTMODEM
OWNER’S MANUAL
(})
Hayes
Microcomputer
Products,
Inc.

NOTICE
Hayes Microcomputer Products, Inc. reserves the right to make improvements in the
product described in this manual at any time and without notice.
Third
edition.
This
manual
is
copyrighted
and
contains
proprietary
information.
All
rights
are
reserved.
This
docu-
ment
may
not,
in
whole
or
part,
be
copied,
photocopied,
reproduced,
translated,
or
reduced
to
any
electronic
medium
or
machine
readable
form
without
prior
consent,
in
writing.
from
Hayes
Microcomputer
Products,
Inc.
€ 1981 by Hayes Microcomputer Products. Inc.
5835 Peachtree Corners East
Norcross, Georgia 30092
[phone]

TABLE OF CONTENTS
Chapter 1:Introduction.... 1-1
DeSCriIDtION. 6 1-1
How lo Use This Manual... 00. 1-3
Chapter 2: Installation... ee. 2-1
FCC Registration 20 en 2-1
Notifying The Telephone Company... 0.0.00... 00000000. cee, O-1
Parts 2-2
Check Power Switch 00 ee 2-3
Volume Control Knob... ee 2-3
Connecting To The Phone Line... ee 2-4
RS-232C Connection. 0 ee 2-4
Configuration Switches . 0000, 2-4
LED Indicators... ne 2-7
Power Connection... ee 2-8
Initial Check Out. es 2-9
Precautions 00 eee 2-9
FCC-Supplied Information For Users .. 0.00.00. 00.0 ee 2-10
Chapter 3: Functional States. ....—.—s—( (i... 3-1
Local Command State... ee, 3-1
On-Line State. ee 3-2
Going From On-line To Command . 0.0... ee 3-2
Escape Code. ee 3-3
Escape Code Operation... 0... ee, 3-4
Terminating Dial Command With ASemicolon..........0..0..0000.. 3-5
Chapter 4: Command Guidelines........................ 4-1
AT Attention Code «0. ee 4-1
AV Command . oo ee, 4-]
Backspace Key 6 es 4.1
Carriage Return. ee 4-1
Missing Parameters... ee 4-1
Command Buffer. 0.0 ee, 4-2
Result Codes 2. es 4-2
Chapter 5: Dialing...) 5-1
Dial Commands... 0. es 5-1
Dial A Number —D Command ....0 0.0000 .0 0 es 5-2
Second Dial Jone—-CommaCommand...........0..0. 000000025. 9-2
Touch-lone* And Pulse Dialing — T AndP Commands............... 9-2
Originating A Call In Answer Mode —R Command ................. 9-3

Redial Last Number — A/ Command..........0..00. 000000000000: 5-3
Return lo Command State. Autodialer — Semicolon Command ....... 5-3
Timing Parameters... es 5-4
Command Sequence .. 0. 5-5
Chapter 6: Automatic Answering...........——.——sis«..... 6-1
Auto-Answer StatuS 00 es 6-1
Switch Set. ee 6-1
Command Setting... 6-2
Difference Between Switch Settings. 00.00.0000. ee 6-2
Auto-Answer PrOCeSS 206. ee, 6-2
Disabling Auto-ANSWwer oe 6-3
ACOMMANG. 00 ey 6-4
Timing Parameters... ne, 6-4
Chapter 7:Commands.................. 7-1
Command List. ee, 7-1
Set Commands 00. es 7-5
Reading ARegister 20 7-6
Changing A Parameter 00.0 ey 7-1
Register Description. 0.0 ee, 7-6
Chapter 8: Configuration Switches......—s—s—s—is—isistst 8-1
Configuration Switches 2,3,4And5 ... 0.0.0.0... 002 8-1
Configuration Switches 1,6 And 7 2.0.0.0. 00.0.0 8-1
Typical SettingS 00 8-3
Chapter 9: Programming Considerations... 9-1
Chapter 10: Background Information................ 10-1
Appendix A: RS-232C Interface Connector Pin
Assignments... A-1
Appendix B: Modular Phone Diagrams, Dial
Pulses, Frequencies... A-2
Appendix C: Block Diagram........—.................... A5
Appendix D: Specifications Summary... ........ A6

Appendix
E:
ASCII
Control
Character
Code
Table...
47
Appendix
F:
Local
Network
With
Two
Smartmodems
.............0...
ee
A-8
Appendix
G:
Monitoring
A
Low
Speed
Data
Line...
AQ
Appendix
H:
Amateur
Radio...................
A-10
Appendix
|:
Return
For
Repair
Procedure...
A-13
Quick Reference Card
Two Year Warranty Card
iI

Chapter 1
INTRODUCTION
DESCRIPTION
The Hayes Stack Smartmodem is a complete high-performance
communications system for smal! computers. It is designed for
use with RS-232C compatible computers and terminals to permit
communication over the telephone lines with other computers or
time-sharing systems.
A unique feature is that the Smartmodem can be program
controlled in any language by ASCII character strings.
This intelligent datacomm system analyzes and executes
commands and in response sends result codes which, at the
users option, can be English words or decimal digits.
Commands may be userentered via a terminal keyboard or
issued under program control.
There are unique “Set” commands that allow the user to select
(and change) various operational parameters such as dialing
speed, how long to watt for a dial tone before beginning to dial
a number, and number of rings to answer on.
The Smartmodem can be used to automatically call and
communicate with time-sharing systems and other computers or
to automatically answer incoming calls from distant systems. A
special design feature is that all circuitry required for
auto-answering and auto-dialing is built Into the unit. This
eliminates the need for any auxiliary equipment and makes the
smartmodem a stand-alone system,
The Smartmodem is approved by the FCC for direct connection
to the telephone lines. Since it is a direct-connect device. the
losses and distortions associated with acoustic couplers are
eliminated.
Unlike most modems, the Hayes Stack Smartmodem can be
connected to any telephone system in the United States since
either Touch-lone* or pulse dialing can be used. Furthermore,
Jouch-Ione and pulse dialing can be combined within a
command, with pulse being used, for example, to access a PBX
board and Touch-lone for dialing an outside number after the
second dial tone is received.
An audio monitor within the Smartmodem permits the user to
follow the progress of the call and be alerted to wrong numbers
and busy signals. If a busy signal is encountered, the user can
enter a repeat command and the Smartmodem automatically
redials the last phone number entered.
1-1

The Smartmodem is completely compatible with Bell 1@3-type
modems. Operation can be in full- or half-duplex with a data rate of
-300 baud. Power-on default options are controlled by the positioning of
seven configuration switches. Four of these configurations can be
overridden by software commands that are userentered or issued
under program control. LED status indicators on the front panel of the
unit provide a visual check of the Smartmodem’'s operational status.
The Smartmodem datacomm system consists of the
Smartmodem unit, a modular telephone cable and a power
pack. Installation is a simple three-step process that involves
plugging in the telephone cable and power pack and
connecting your system's RS-232C interface cable to the
RS-232C connector installed on the back panel of the
smartmodem.
The Smartmodem can be used in three operational modes, .e.,
connection to a terminal, computer, or receive-only device.
Although the Smartmodem is an intelligent system, there are just
some things it was not designed to do:
1) The Smartmodem will not and cannot be modified to operate
at speeds higher than 3@0 baud.
2) The Smartmodem cannot detect dial tones and distant busy
or ringing signals, therefore, it cannot tell if the call it made
was answered unless it connects with another modem.
3) Commands given to the Smartmodem must be ASCII coded
at baud rates between 118 baud and 1200 baud. Once “on-line”
any code at any speed from @ to 380 baud may be used.
4) Two Smartmodems cannot be connected back to back
(RS-232C to RS-232C) even with a cross-over cable. They can
be directly connected with a modular cable as shown below.
——-{[_ JC] MODULAR
CABLE
MTEL ETT
Ss
TERMINAL
RS-232-C
COMPUTER
5) The monitor speaker only allows you to monitor the progress
of a call. You cannot talk back if a person answers. It is not
a speaker phone.
1-2

HOW TO USE
THIS MANUAL
This manual provides complete installation and operation
procedures for Smartmodem owners. It does not include
technical information about the construction or design of the
equipment. The material in this manual is organized so that you
only have to do a minimum amount of reading before you begin
using your Smartmodem. You certainly do not have to (nor is it
expected that you will) read this manual from cover to cover
before starting operation. In fact, as is explained here, there are
some chapters that many users may never reference — except
out of curiosity,
Chapter 2, Installation, should be read by everyone. In addition.
it is recommended that ail users read Chapters 3 and 4. Then
depending upon whether you want to initially use your Smart-
modem for dialing or answering proceed to Chapter 5 or 6.
Chapter 2 contains all pertinent FCC-related information,
including the notification procedures that must be followed
before connecting your Smartmodem to the phone lines. The
remainder of this chapter gives you step-by-step installation
instructions and a general introduction to the functions of the
various design features of the Smartmodem.
Chapter 3 introduces you to the two major functional states -
i.e, local command and on-line — in which the Smartmodem
operates. This background information explains what your
Smartmodem does in each functional state and how you can
force it to move from one state to the other.
Chapter 4 provides you with guidelines to follow in sending
commands to the Smartmodem. Also introduced are the result
codes which the Smartmodem sends in response to your
commands.
Now with your Smartmodem installed and with the background
information gained from Chapters 3 and 4 you are ready to put
your Smartmodem to work.
Chapter 5 is a stand-alone chapter that gives complete
instructions for executing dialing commands/operations. If you are
only interested in auto-answering, Skip Chapter 5 and go to
Chapter 6.
Chapter 6 is also a stand-alone chapter, but information
contained here provides you with complete instructions for
utilizing the auto-answering capability of the Smartmodem,
Chapter 7 lists and defines all commands that can be used
with the Smartmodem. Of course. by the time you have finished
Chapters 2-6 you will already be familiar with the most frequently
used commands. Don't let the size of this chapter fool you:
some of the commands listed you will rarely. if ever. use. In fact.
most users will probably. at least initially only use this chapter
1-3

as a reference in changing values assigned to the Set registers
or operational parameters, e.g., full-duplex to half-duplex. As you
become more adventuresome, however, you may want to
experiment with some of these other commands just to see
what other capabilities your Smartmodem has.
Chapter 8 gives more detailed information on the configuration
switches and various settings for these switches. In Chapter 2 you
are introduced to the configuration switches and the factory setting
for these switches. With the switches in the factory setting the
Smartmodem will function effectively whether it is connected to a
computer, terminal or printer. So, you may want to skip Chapter 8.
However, if you are interested in learning more about these switches
and possible alternate settings, then you will find the facts in
Chapter 8.
Chapter 9 is specifically for users who plan to utilize the
Smartmodem under program control. Since the Smartmodem
can be program controlled in any language, specific programs
are not included in this manual because requirements differ with
each type of computer. This chapter does, however, provide you
with specific programming considerations that will assist you in
program development.
Chapter 10, Background Information, is included to give you a
brief history of the develooment of modems.
The appendices to this manual contain supplementary information
and notes on some special applications. The applications
included are:
¢ Local Network with Two Smartmodems, Appendix F;
¢ Monitoring a Low Speed Data Line, Appendix G;
« Amateur Radio, Appendix H.
"Trademark of American Telephone and Telegraph.
1-4

Chapter 2
INSTALLATION
FCC
REGISTRATION
NOTIFYING
THE
TELEPHONE
COMPANY
This chapter contains the information necessary to get your
Smartmodem ready for use. Instructions for notifying the
telephone company and pertinent FCC-related information are
presented.
Step-by-step installation instructions are provided with illustrations
to assist you in this three-step process. Combined with the
installation instructions are brief descriptions of the various
design features of the Smartmodem. The intent is that when you
have completed this chapter, you will not only have your
sSmartmodem installed, but will also be generally familiar with the
function of each component.
The Hayes Stack Smartmodem system is registered with the
Federal Communications Commission (FCC) which places three
restrictions on its use:
« The Smartmodem cannot be connected to a party line or pay
telephone.
« The telephone company must be notified that an FCC
registered device |s being installed.
¢« Hayes Microcomputer Products must make any necessary
repairs to the Smartmodem in order to maintain valid FCC
registration.
« If you experience trouble with your telephone during or after
installation, disconnect the Smartmodem to determine if it is
causing the difficulty. For further details on what to do if the
Smartmodem appears to be the cause see the Precautions
section in this chapter.
The telephone company will need the following information
before the Smartmodem is installed:
« The telephone number to which it is to be connected.
¢ The FCC registration number which is:
BFJ9D9-68737-DME
« The ringer equivalence: @.4B.
¢ The Smartmodem needs to be connected to one of the
following standard modular jacks:
USOC-RJ11W USOC-RJ11C
USOC-RJ12W USOC-RJ12C
USOC-RJ13W USOC-RJ13C
If you plan to connect the Smartmodem to several different
telephone lines, give the telephone company a list of the
numbers. This avoids having to notify them each time the
Smartmodem is moved. The telephone company must also be
notified when the Smartmodem is permanently removed from a
2-1

PARTS
4 4 et
telephone line. If the local telephone company has questions,
refer them to Hayes Microcomputer Products, Inc.. Norcross.
Georgia.
In addition to this manual, the Hayes Stack Smartmodem data
communications system consists of three parts (see Figure 1):
1. Smartmodem unit
2. Power Pack
3. One modular telephone cable to connect the Smartmodem
to the telephone line.
Remove each part from the molded container and check to
make certain the Smartmodem system is complete and
undamaged.
Ty ay
ee
ry oranr Se
-& EEBE SK.
oe ee,
D9. COGS.
ty Te es gs
Nw Oe, ,
o . .
°°
ey.
”
o
Figure 1
Smartmodem System Parts
NOTE: If you are connecting the Smartmodem to a computer.
you will need an RS-232C serial port, an RS-232C cable with a
DB-25 connector and software that will permit an interface
between the computer and the Smartmodem. If your computer
does not have this equipment. consult your computer reference
manual or your computer dealer and obtain the appropriate
RS-232C equipment and software. Install the RS-232C equipment
and software according to the instructions provided in your
computer reference manual or provided by your dealer.
2-2

NOTE: If the device (computer, terminal or printer) to which the
Smartmodem is to be connected does not have a DB-25
connector, it will be necessary to obtain an adapter that will
permit connection with the DB-25 female connector installed on
the back panel of the Smartmodem. This is required to set up
the RS-232C connection.
CHECK Examine the back panel of the Smartmodem unit and consult
POWER Figure 2 for identification of the connectors, power switch and
SWITCH volume control.
POWER POWER RS-232C TELEPHONE VOLUME
SWITCH CONNECTION CONNECTION CONNECTION CONTROL
KNOB
Figure 2
Smartmodem Back Panel
There is only one toggle power switch located on the back
panel of the Smartmodem. BEFORE PROCEEDING WITH THIS
INSTALLATION, BE CERTAIN THE SMARTMODEM POWER
SWITCH IS TURNED OFF (i.e. DOWN POSITION) AND POWER
TO YOUR COMPUTER, TERMINAL OR PRINTER IS OFF.
VOLUME The Volume Control knob allows you to control the volume from
CONTROL the audio monitor or speaker installed in the Smartmodem. For
KNOB example, when the Smartmodem is used for automatic dialing,
the audio monitor allows you to listen to the progress of the call.
You will hear the number being dialed; the phone ring: and a
busy signal, if one is given.
When the Volume Control knob is turned completely
counterclockwise, volume is off. For initial setting it is suggested
that this control knob be turned slightly clockwise. Then during
actual operation, adjust the volume to the desired level or turn it
off.
2-3

CONNECTING
TO THE
PHONE LINE
RS-232C
CONNECTION
CONFIGU-
RATION
SWITCHES
After the telephone company has been notified according to the
instructions previously specified, follow this procedure to connect
the Smartmodem to the phone line.
With the gold contacts up, plug one end of the modular
telephone cable into the phone connection on the back panel of
the Smartmodem. The cable will slide in easily and snap in
place when the connection is made.
Next. plug the remaining end of the telephone cate into a
telephone wall jack just as you would a modular telephone.
lf you are making a single line connection, the cable must be
inserted in an RJ11C or RJ11W wall jack; any other connection
for single line phone installations could cause trouble with the
phone lines or damage the Smartmodem.
If the installation is for multiple key line installations the cable
must be connected to an RU12W, RJ12C, RJ13W or RU13C
phone jack. Detailed explanations of this procedure are usually
found in the information pages in the front of the telephone
book. Appendix B of this manual contains diagrams of the
modular phone jack connections.
NOTE: No wiring changes are required if you are connecting
your Smartmodem to a terminal or to a computer that is wired
as DTE (Data Terminal Equipment). (If you are not certain
how your equipment is wired, check the manual supplied by the
manufacturer of the equipment or contact your computer dealer)
lf your computer is wired as DCE (Data Communications
Equipment), you must first make the following aajustments:
1. Use only pins 2. 3 and 7 for the RS-232C interface.
2. Reverse pins 2 and 3 in the RS-232C connector.
Now to make the RS-232C connection from your computer,
terminal or printer to the Smartmodem, insert the male DB-25-P
connector in the DB-25-S female connector located on the back
panel of the Smartmodem. This connection can only be made
one way: if the connector does not fit, turn it upside down and
insert in the female DB-25-S connector. Connect the other end
of the RS-232C cable to your terminal, computer or printer.
Consult Appendix A in this manual for interface connector pin
assignments. .
The setting of the configuration switches establishes the operating
parameters for the Smartmodem whenever power is turned on, 1.e.,
how the Smartmodem will operate from a “cold start.”

Once
power
is
turned
on,
many
of
these
operating
parameters,
or
default
values,
can
be
overridden
by
commands
to
the
Smartmodem.
Note,
however,
if
power
is
turned
off
and
then
on,
or
if
the
Smartmodem
is
sent
a
reset
command,
the
Smartmodem
will
revert
to
the
operating
parameters
established
by
the
switch
settings.
You
will
find
out
more
about
this
as
it
relates
to
dialing,
Chapter
5;
auto-answer,
Chapter
6;
and
all
commands,
Chapter
7
The configuration switches are located behind the front panel of the
Smartmodem. To reach the configuration switches, you must remove
the end cap from the front panel. (Note that the end cap fits snugly
into the front panel.) Firmly hold or support the unit and carefully
remove the end cap according to the following procedures.
Figure 3a
Insert the tip of a small tool in the notch as shown above. Twist
slightly to release the end cap.
Figure 3b
Carefully
remove
the
end
cap
from
the
Smartmodem.
2-5

The configuration switches are numbered 1 through 8 (switch 8 is
not used and its setting does not matter).
The factory setting for the configuration switches and the functions
established by these settings are defined in Table 1. (Note that the
position of the switches is defined as being either UP or DOWN.)
Check the position of the configuration switches on your
smartmodem and make any adjustments necessary to have the
settings correspond to the factory setting in Table 1 and illustrated in
Figure 4.
TABLE 1
CONFIGURATION SWITCHES
SWITCH NO. FACTORY SETTING FUNCTION
1 DOWN Enables Smartmodem to execute commands
by providing signal that the data terminal is
ready to receive or send data.
2 UP Smartmodem responds to commands with
verbose (English words) result codes.
3 DOWN Result codes are sent by Smartmodem to
your terminal or computer.
4 UP Smartmodem will echo characters while in the
command state. That is, commands you send
to the Smartmodem will be sent back
(echoed) to your terminal screen.
5 DOWN Smartmodem will not automatically answer the
phone when it rings.
6 DOWN Forces computer to accept locally echoed
characters and result codes from
Smartmodem.
7 UP Setting used for connection to an RJ11
modular telephone jack (single line
connection).
8 DOES NOT Switch not used.
MATTER
gill Hn
Hil
al
i Hifi in| 7 1
AU
Ml
=
ih
=
Figure 4
Configuration Switches
2-6

The
Smartmodem
will
function
effectively
in
any
of
the
operational
modes
(i.e.,
with
a
terminal,
computer
or
printer)
when
the
configuration
switches
are
positioned
according
to
the
factory
setting
shown
in
Table
1.
(For
more
information
on
the
configuration
switches
and
typical
settings
for
various
modes
of
operation,
see
Chapter
8.)
When
the
positions
of
the
configuration
switches
have
been
checked
and
are
in
the
factory
setting,
carefully
replace
the
end
cap
on
the
front
panel
of
the
Smartmodem.
LED
The
front
panel
of
the
Smartmodem
contains
seven
indicator
INDICATOR
lights
that
visually
identify
the
status
of
the
Smartmodem
(see
LIGHTS
Figure
5).
ee
Smartmodem
Figure 5
Smartmodem Front Panel
From
right
to
left,
the
indicator
lights
are:
MR =Modem Ready
TR = Terminal Ready
SD =Send Data
RD = Receive Data
OH = Off Hook
CD = Carrier Detect
AA =Auto Answer Mode
MR
(Modem
Ready)
indicator
light
is
illuminated
at
all
times
when
the
Smartmodem
is
powered
up.
TR
(Terminal
Ready)
indicator
lights
to
show
a
signal
has
been
given
to
the
Smartmodem
that
the
data
terminal
is
ready
to
receive
or
send
data;
this
signal
enables
the
Smartmodem
to
execute
commands.
The
position
of
configuration
switch
1
determines
when
the
TR
indicator
will
light.
When
configuration
switch
17
is
in
the
DOWN
position,
the
TR
indicator
light
will
illuminate
and
remain
lit
at
all
times
while
the
Smartmodem
is
powered
up.
2-/

POWER
CONNECTION
When configuration switch 1 is set in the UP position. the TR light will
illuminate and remain lit only when the Smartmodem is powered up
and power to your computer or terminal is on. This setting can only be
used if your data terminal supports the RS-232C Data Terminal Ready
lead (pin 20). See Chapter 8 for more on this.
SD (Send Data) indicator flashes when data is sent from the
RS-232C port to the Smartmodem (i.e.. when commands are
sent to the Smartmodem or data is transmitted to a distant
computer).
RD (Receive Data) light flashes when data received from a
distant computer or terminal is sent from the Smartmodem to the
RS-232C port. In full-duplex (with echo), this light will pulsate
when commands are sent to the Smartmodem since the
information sent is also returned or echoed. It will also flash
when the Smartmodem sends result codes.
OH (Off Hook) indicates if the Smartmodem has “picked up”
the telephone. The OH indicator light is illuminated when the
smartmodem is using the telephone line, otherwise this light
is off.
CD (Carrier Detect) shows if the Smartmodem has detected a
carrier signal from a distant modem. When the Smartmodem
recognizes a carrier signal, the CD indicator will light. When no
detectable carrier is present, or if the distant modem hangs up,
this light will be off,
AA (Auto-Answer) identifies the state of the auto-answer mode if the
Smartmodem is set (via the position of configuration switch 5 or by
command) to automatically answer, the AA light will be Illuminated,
Then, when the phone rings, the light will go off during each ring and
the Smartmodem will automatically answer the phone after the
number of rings specified.
If the Smartmodem is set to not answer the phone (..€.,
configuration switch 5 is in the DOWN position and no command
override has been given), the AA light will be off. Then when the
telephone rings, the AA indicator will light during each ring. In this
state the Smartmodem requires a command to answer the phone.
Insert the power cable connector in the power inlet on the back
panel of the Smartmodem. Next, connect the power pack plug
to the electrical outlet. Flip the toggle power switch ON (.e.,
UP position).
In response the MR and TR indicator lights will illuminate indicating
the Smartmodem is ready, (If configuration switch 1 is notin the
2-8

INITIAL
CHECK OUT
PRECAUTIONS
factory setting —L.e., is in the UP position — the TR indicator will not
light until power to the computer or terminal is turned on.)
Turn power to the terminal or computer ON.
The Smartmodem data communications system is now
completely installed.
If the Smartmodem is attached to a computer that is being
used as a terminal, before entering data you must enter the
appropriate command listed in your computer reference manual
to access the RS-232C port that the Smartmodem is connected
to.
Jo determine if the Smartmodem Is listening:
Depress: RETURN KEY = (while entering data, the RD and
SD indicator lights will flash)
Enter: AT
Depress: RETURN KEY
If everything is functioning properly, the Smartmodem will
respond with “OK” and await your command.
lf something is wrong, there will be no message and the RD
and SD indicator lights will not flash when data is entered.
Consult your dealer to see if the unit should be returned for
repair. If so, follow the Return for Repair Procedure specified in
Appendix I of this manual.
Disconnect the Smartmodem if you experience trouble with the
telephone line after installation. If the Smartmodem is responsible
for the trouble on the line, do not use it until it has been
repaired by Hayes Microcomputer Products. The telephone
company Is not responsible for disturbances caused by
non-teleohone company equipment.
The telephone company may change their equipment and is
under no obligation to ensure that the new equipment will be
compatible with the Hayes Smartmodem. However, it is unlikely
that any changes in telephone equipment will make the
smartmodem unusable. This is because the interface between
the Smartmodem and the telephone line is functionally identical
to the interface between millions of standard telephones in use
and the telephone line.
2-9