Radio Shack Modem I TRS-80 User manual

Modem I
atalog Number 26-1172
MICRO
COMPUTER
SYSTEM
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CUSTOM MANUFACTURED IN U.S.A. BY RADIO SHACK, ADIVISION OF TANDY CORPORATION

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sis

Introduction
The Modem Iis aself-contained, fsk (Frequency Shift Keying) telephone
interface. It enables your computer to communicate with other computers via
ordinary telephone lines. The Modem Iis compatible with all trs-so models
(except Level Iversions of the Model Iand Model III) and with other rs-232-c
standard devices.
Its special features include:
•Sends/receives at 0-300 baud for compatibility with most time-shared
computer systems.
•Selectable originate/answer mode for operation in "remote" or "host"
terminal applications.
•Full duplex operation allows simultaneous communication between modems.
•Direct (non-acoustic) connection to phone lines helps ensure alow error rate.
•NORMal/CASsette switch lets you use rs-232-c equipped computers and trs-80
Model ILevel II computers which do not have an rs-232-c interface. Select
norm for rs-232-c use; cass for use with the cassette interface of Model I
Level II Computers. Cassette use requires optional/extra "Cassette-Comm"
software (Radio Shack Cat. No. 26-1 139) and acassette cable (26-3009).
•Bell 103 compatible.
Note: When using the Cassette Comm software, communications will not be in
atrue full duplex mode. For further details, see the Cassette Comm instruction
manual.
Important Note
Before connecting your Modem Ito the phone lines, you must notify your
local telephone company of the:
Manufacturer: Radio Shack
Model: Modem l(#26-1172
USOC Number: RJ11C
FCC Number: AA099R-69525-DM-N
Ringer Equivalence Number (REN): 0.0B
This information also appears on the bottom of the Modem.
The Modem Imust not be connected to:
[x] Coin-operated phones
[x] Party-line phones
[x] Multiple-line phones
Modem IOwner's Manual: Copyright ©1981 Tandy Corporation. All rights reserved.

Installation
Modem/Telephone Connection
Figure 1shows the connection of aModem Ito telephone lines using the new
modular connectors. If your telephone has this type of connection, attach your
Modem Ias shown.
If your telephone has the older style four-prong connection (see Figure 2), you
will need an adapter which allows the Modem Ito be used in parallel with your
telephone. Radio Shack sells this type of adapter, Cat. No. 279-360.
If your telephone is wired directly to the wall as in Figure 3, you must contact
the telephone company and have them install modular connections. Be aware
however, that you will be charged for this service.
After connecting the telephone, make sure that the mode switch on the Modem
is off. Your telephone should be operating normally now.
AC Connection
Connect the ac adapter to the ac jack on the Modem's rear panel and to an
electrical wall outlet.
Note: Use only the supplied, UL-listed adapter. The use of any other adapter
could damage the Modem.
Modem/Computer Connection via
RS-232-C Interface
For most applications, you will use an rs-232-c equipped computer. Table 1
summarizes the cable and connection requirements for rs-232-c equipped
trs-80's. Using the table, select the appropriate connector for your computer.
Connect the computer's rs-232-c interface to the specified connection point on
the Modem.
TRS-80 Model Cable Connection Point
TRS-80 Modem I
Model 1, Level II 26-1145* Card-Edge
on Exp/Int
DB-25
"RS232C"
Model II 26-4403 DB-25
"CHANNEL A/B"
DB-25
"RS232C"
Model III 26 1408 DB-25
Serial I/O
DB-25
"RS232C"
Color Computer 26-3020 DIN
Serial I/O
DIN
"RS232/CASS"
This is the RS-232-C interface board. The cable is included.
Table 1. RS-232-C Cable Identification and Connection

If your telephone hook-up looks like this:
Connect like this:
Figure 1. Connection to Modular Phone Jacks.

Modem/Computer Connection via
Cassette Interface
Note: When using the Cassette Comm software, communications will not be in
atrue full duplex mode. For further details, see the Cassette Comm instruction
manual.
If you have aModel ILevel II computer which is not equipped with an rs-232-c
interface board, you may use the cassette interface of your computer for serial
communications with the Modem. To do this, you will need to buy the
"Cassette-Comm" software and the appropriate cable (Cat. Nos. 26-1139 and
26-3009, respectively).
Connect the cable to the tape connector on your computer and to the rs-232/cass
connector on the Modem.
Note: The Model III cassette circuitry cannot be used for serial communications
with the Modem.
Controls and Connectors
Refer to Figure 4.
©mode Switch Selects either ORiGinate or ANSwer mode. Note: With the
Modem connected, your phones are available for conversational use only
when the mode switch is off. So be sure to select mode off when you are
not using the Modem.
©On Power Light Remains lit while the Modem is ''on."
CD. (Carrier Detect) Light Lights and remains lit while a"carrier tone" is
being received via phone lines from another modem.
(7) RS-232C Standard db-25 jack for connection to rs-232-c interface of Models
I, II and III.
(s) rs-232/cass This four-pin din jack allows connection to the RS-232-c
interface of the trs-so Color Computer, or to the Model ILevel II cassette
interface.
(jj) power ac adapter plug goes here.
(7) phone Modular-type jack for telephone line cord.
(a) NORMal/cASsette Switch For use with rs-232-c equipped computers, use
norm position. For use with cassette interface of Model ILevel II computer,
use cass position.
(9) to wall This modular-type plug connects to the telephofie wall jack in
place of the telephone cord.

Top View
Rear View
Figure 4. Identification of Controls and Connectors.

General Operation
The Modem Iaccepts digital data from your computer and generates tones
which can be sent over the telephone lines to another Modem. The Modem Ican
also receive tones from the telephone line and change them back to digital data.
(The Frequency Shift Keying method is used. For details, see Specifications.)
Baud Rate
The speed at which the Modem receives and transmits these tones is called
the baud rate. The Modem Ican send and receive at baud rates from 0-300. 300
baud is standard for most time-shared systems, but some may use 110, 150, or
other rates. Before using the Modem, be sure your computer and the host
computer are set to the same baud rate (0-300).
Originate vs. Answer
The Modem Ican operate in either originate or answer mode. Electrically, the
mode switch determines which set of receive and transmit tones the Modem will
respond to. For communications to take place, one modem must be in the
originate mode and the other in the answer mode.
Normally, when you dial a"host" computer, your Modem should be in the
originate mode. When you receive acall from a"remote" computer, your
Modem should be in the answer mode. See Figure 5.
RS-232 Communications
For communication between computers and computer-related equipment, the
most widely used standard is the RS-232C This allows use of cables of up to
50 feet in length between the Modem and the computer. The Modem has two
rs-232-c connectors: astandard db-25 connector (labeled RS-232C) which is used
with the majority of computers, and the four-pin din connector (labeled RS-232),
for use with the trs-80 Color Computer.
Cassette Communications
The Modem 1contains special circuitry for communications with the cassette
interface of Model ILevel II computers. To use this method, youTl need the
"Cassette-Comm" software and aspecial cable (see Installation).

Host Terminal
ORiGinate
Mode
User places call.
Figure 5. Originate/Answer Mode Difference.

Operating Procedures
First find out the communications conventions of the computer or other device
with which you are going to communicate. In particular, find out the:
Baud Rate
Word Length
Parity
Number of Stop Bits
Who will use originate mode, who will use answer mode
Set up your computer accordingly, and set the Modem's mode switch
accordingly.
A. Originate Mode
1. With the mode switch off, dial the number of the "host" computer.
2. When you hear the carrier tone, flip the mode switch to ORiGinate and hang
up the phone.
3. When the Carrier Detect (cd) light comes on, you may start communicating.
When communications are finished, be sure to sign off. (The sign-off will
depend on the "host" computer, however, bye or goodbye is commonly
used.)
4. After signing off, wait until the Carrier Detect light (cd) goes off, then flip
the mode switch to off.
B. Answer Mode
1
.
Wait for the "remote" computer operator to call you,
2. Upon receiving the call, flip the mode switch to ANSwer and hang up nfoe
phone.
3. When the Carrier Detect (cd) light comes on, begin data comimiMicatons.
4. When finished with the data transfer, set tfie mode switch to off.
10

When Something Goes Wrong
If you have trouble (garbled data, intermittent errors, etc.), check for the
following:
1. The phone connection should be clean and noise-free.
2. There should be no one talking on the telephone line.
3. The phone and all extension phones should be on-the-hook.
4. The baud rate of the terminal should be less than or equal to 300.
Troubleshooting Chart
Symptom Problem/Solution
Carrier Detect light off
AC Adapter is not plugged in; plug in.
Telephone connections; check connections and refer to
the Installation section.
mode switch is not in proper position; refer to the
General Operation section.
Modem at other end is not compatible; modem should
be aBell 103 or equivalent.
Garbled Display
Phone not hung up; hang up phone.
Communications protocol may be set incorrectly (baud
rate, word length, parity, stop bits); check and change if
necessary.
11

Specifications
Receive
Frequencies
A. Answer
Mark 1270 Hz;
Space 1070 Hz
B. Originate
Mark 2225 Hz;
Space 2025 Hz
Transmit
Frequencies
A. Answer
Mark 2225 Hz;
Space 2025 Hz
B. Originate
Mark 1270 Hz;
Space 1070 Hz
Transmit
Power -10dBm, ±1dB
Receive
Sensitivity -45dBm
Baud Rate 300
Operating
Temperature 55°F-85°F
(12.8°C-29.4°C)
Electrical
Requirements 15VACat300ma
supplied by ul
listed ac adapter
Size 6.5" x7.5" x2"
(16.5x19.1 x5.1
cm)
12

RADIO SHACK, ADIVISION OF TANDY CORPORATION
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