MFJ MFJ-1270C User guide

o 15.838 Class B computing device: information to user.
This equipment generates and uses radio frequency energy and if not installed
and used properly, that is, in strict accordance with the manufacturer's
instructions, may cause interference to radio and television reception. It has
been type tested and found to comply with the limits for a Class B computing
device in accordance with the specifications in subpart J of Part 15 of FCC
Rules, which are designed to provide reasonable protection against such
interference in a residential installation. However, there is no guarantee that
interference will not occur in a particular installation. If this equipment does
cause interference to radio or television reception, which can be determined by
turning the equipment off and on, the user is encouraged to try to correct the
interference by one or more of the following measure:
Reorient the receiving antenna
Relocate the computer with respect to the receiver
Move the computer away from the receiver
Plug the computer into a different outlet so that computer and receiver are
on different branch circuits.
If necessary, the user should consult the dealer or an experienced radio/television
technician for additional suggestions. The user may find the following booklet
prepared by the Federal Communications Commission helpful:
"How to Identify and Resolve Radio-TV Interference Problems".
This booklet is available from the U.S. Government Printing Office,
Washington, DC 20402, Stock No. 004-000-00345-4.
Warning-When connecting this device to your computer,
shielded interface cables must be used.

i
MFJ ENTERPRISES, INC.
Model MFJ-1270C/1274C
Packet Radio Controller
Revision 10
SYSTEM MANUAL
Fourth Edition
(c) Copyright 1993, MFJ Enterprises, Inc.

ii
TNC 2 SOFTWARE SOURCE CODE and TNC FIRMWARE
Copyright (c) 1985 - 1993
Systek
MFJ-1270C/1274C SOFTWARE SOURCE CODE and FIRMWARE
Copyright (c) 1993
MFJ Enterprises, Inc.
All rights reserved.
Reproduction or translation of any part of this work beyond that permitted by
Sections 107 or 108 of the 1976 United States Copyright Act (or its legal
successor) without the express permission of the copyright owner is unlawful
except as noted below. Requests for permission to copy or for further
information should be addressed to MFJ Enterprises, Inc. P. O. Box 494,
Mississippi State, MS 39762, USA.
The information contained in this document has been carefully checked and is
believed to be entirely reliable. However, no responsibility is assumed for
inaccuracies. MFJ Enterprises, Inc. reserves the right to make changes to any
product to improve reliability, function or design without obligation to
purchasers of previous equipment. MFJ Enterprises, Inc. does not assume
any liability arising out of the application or use of any product or circuit
described herein; neither does it convey any license under its patent rights to
others.

MFJ-1270C/1274C MANUAL TABLE OF CONTENTS
iii
TABLE OF CONTENTS
TABLE OF CONTENTS.............................................................................iii
INTRODUCTION .......................................................................................1
Items supplied with MFJ TNC package.........................................2
Optional items available for the MFJ TNC....................................3
COMPUTER INTERFACING ....................................................................4
MFJ Terminal Software Starter Packs ...........................................4
Computer Interfacing with MFJ Starter Packs.................5
Computer Interface without MFJ Starter Pack ................5
Serial Port Signals..........................................................................5
Computers with Specific Serial Interfaces.......................7
Apple Macintosh ...............................................7
Commodore C64, C128 and VIC-20.................8
IBM PCjr...........................................................9
Radio Shack Color Computer............................9
Radio Shack Model 100/102 and NEC 8201 ....9
IBM PC/XT/AT/386/486 and compatibles
Computer...........................................................10
Other Computers with Non-standard Serial Ports............12
Terminal Software Requirements...................................................12
Apple Macintosh .............................................................13
Apple II, II+, IIe, IIc........................................................13
Commodore C64, C128 and VIC-20 ...............................13
IBM PCjr.........................................................................14
IBM PC and Compatible Computers...............................14
Radio Shack Color Computer..........................................15
Radio Shack Model 100/102 and NEC 8201...................15
MFJ TNC Serial Port Pin Functions.............................................15
Computer Baud Rate......................................................................16
Verifying Serial Port Operation .....................................................17
RADIO INTERFACING .............................................................................20
MFJ TNC Radio Port....................................................................20
Radio Port Connection ....................................................21
Handheld Radio Connection............................................21
RADIO INTERFACING METHODS ...........................................23
Method 1: Direct Connection to Microphone and
Speaker ............................................................................23
Transmit Audio Level Adjustment for
Method I Interface.............................................24
Setting the Receiver Audio Input Level...........................25

MFJ-1270C/1274C MANUAL TABLE OF CONTENTS
iv
Method 2: Accessory Jack or Interface Box
Connection.......................................................................25
Transmit Audio Level Adjustment for
Interface Method II ...........................................27
Receiver Audio Setting .....................................28
Monitor Speaker Connection...........................................29
GETTING STARTED .................................................................................30
First Steps ......................................................................................30
Basic Parameters Setup ...................................................31
Serial Port Configuration ...............................................................31
Parity and Word Length ..................................................32
Echos ...............................................................................33
New Lines and Line Wrapping........................................33
Tuning Indicator (MFJ-1274C) .....................................................34
PACKET OPERATION ...............................................................34
VHF Packet .....................................................................34
A Connecting and Disconnecting Exercise .......35
Digipeating........................................................37
Unsuccessful Connections.................................38
Monitoring Channel Activity.............................39
Your First Packet QSO......................................40
Starting the QSO ...............................................41
Digipeating........................................................42
Monitoring on the Air .......................................43
Special Input Characters..................................................43
HF Packet Basic Operation .............................................46
HF Packet Operation Hints: ..............................47
FAX OPERATION........................................................................47
FAX FREQUENCY ........................................................48
FAX STATION FREQUENCIES.....................49
Other FAX Frequencies.....................................49
ADVANCED PACKET OPERATION .......................................................50
Special Characters .........................................................................50
Packet Operating Modes ..............................................................................52
Command Mode ............................................................................52
Entering Data-Transfer Modes ........................................53
Converse Mode................................................................54
Transparent Mode............................................................56
Flow Control..................................................................................57
XON/XOFF Flow Control...............................................58
Hardware Flow Control ...................................................59
Type-in Flow Control ......................................................59

MFJ-1270C/1274C MANUAL TABLE OF CONTENTS
v
Detail VHF Packet Operation ........................................................60
Station Identification .......................................................60
Automatic Operations......................................................61
Unattended Operations ....................................................62
Packet Formatting............................................................62
Packet Timing Functions .................................................64
Transmit Timing................................................64
Packet Timing ...................................................65
Radio Baud Rate ...............................................66
Special Protocol Times .....................................67
Monitor Functions..........................................................................68
Real-Time Clock and Time Stamping............................................70
Multi-Connect Guide .....................................................................70
Setting the MFJ TNC to Normal Operation.....................70
How to Invoke Multi-Connect? .......................................71
Easy-Mail Mailbox ........................................................................72
Set Up your Easy-Mail Mailbox......................................72
Mailbox Operation ..........................................................78
Additional Mailbox Features.............................83
Forwarding..........................................83
Eliciting Reverse Forwards.................84
Remote Heard Log..............................84
Chat Mode: .........................................85
Page SYSOP .......................................85
Remote SYSOP...................................85
Mailbox CText....................................85
Idle Timeout........................................85
Abort:..................................................86
Mailbox Messages .........................................................................86
Slotting and Acknowledgment Priority ........................................................88
Description.....................................................................................89
New Parameters...............................................................90
Other Related Parameters ................................................93
Initial Parameter Settings Summary ................................94
What to Expect ................................................................95
Packet Picture Transfer..................................................................96
Receiving Packet Pictures on Printer...............................97
Packet Picture transfer to the computer screen................97
Detail HF Packet Operation...........................................................98
Radio Setup for HF Packet Operation .............................98
HF Packet Operation......................................................................102
MFJ TNC KISS MODE AND HOST MODE ...............................109

MFJ-1270C/1274C MANUAL TABLE OF CONTENTS
vi
KISS Interface for TCP/IP...............................................109
OPERATION COMMANDS.......................................................................111
Entering Commands.......................................................................111
COMMAND NAME .......................................................112
Default...............................................................113
Parameters.........................................................113
Remarks.............................................................114
TNC MESSAGES........................................................................................196
Packet Messages ............................................................................196
Mailbox Messages .........................................................................197
Command Mode Error Messages.................................................................199
Link Status Messages.....................................................................201
HARDWARE...............................................................................................204
MFJ-TNC Specifications...............................................204
General Description .......................................................................206
Detailed Circuit Description ..........................................................206
Oscillator .........................................................................206
Dividers and Baud-rate Generator...................................207
CPU Complex..................................................................207
Serial Interface ................................................................208
Watch-dog Timer.............................................................208
Modem ............................................................................209
Power Supply...................................................................209
RS-232C Handshaking Protocol ....................................................210
Jumper Functions...........................................................................211
HF Tuning Indicator ......................................................................217
TROUBLESHOOTING...............................................................................218
General Tests .................................................................................218
Step 1: Power Supply .....................................................218
Step 2: Obvious Problems ..............................................219
Step 3: Assembly Problems ............................................219
Step 4: Cabling Problems ...............................................219
Specific Symptoms ........................................................................220
Symptom: TNC appears dead ........................................................220
Oscillator and Reset Circuits .........................................................220
Digital Logic Lines ........................................................................220
Symptom: Modem won't calibrate or key transmitter. ...................221
Symptom: Uncopyable transmitted or received packets ................222
Terminal Interface Troubleshooting.............................................................222
Symptom: MFJ-TNC won't sign on to the terminal. ......................222
Symptom: The MFJ-TNC appears to be signing on but only
gibberish is printed on the terminal................................................223

MFJ-1270C/1274C MANUAL TABLE OF CONTENTS
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Symptom: The MFJ-TNC signs on OK but won't accept
commands. .....................................................................................223
Symptom: The MFJ-TNC appears to have "locked-up" i.e. not
responding to any commands.........................................................224
PACKET RADIO PROTOCOL...................................................................225
Explanation of Protocol .................................................................225
Physical Layer .................................................................225
Data Link Layer...............................................................226
HDLC Frames .................................................................226
AX.25 Level Two ..........................................................................227
Channel Use and Timing Functions .............................................................230
Channel Flow Control ..................................................................................232
RADIO HOOKUP .......................................................................................233
MODEM CALIBRATION ..........................................................................234
Modulator and Demodulator Frequency Calibration .....................234
Method I ..........................................................................234
HF Modem ........................................................234
VHF Modem .....................................................235
METHOD II ....................................................................235
Set Modulator Tones Using Built-in Calibration
Software...........................................................................236
Demodulator Center Frequency Alignment .....................237
Tuning Indicator Alignment ............................................238
MFJ-TNC Adjustment Location Map..........................................239
AUDIO OUTPUT CALIBRATION..............................................241
Audio Output Level Adjustment Procedure...................................241
HF RADIO ALIGNMENT ..........................................................................243
First method: NOISE AVERAGE FREQUENCY.........................243
Second method: FILTER SKIRT AVERAGE FREQUENCY ......243
MFJ-TNC 2400 PACKET OPERATION..................................................245
2400 Packet Operation Setup.........................................................245
B. Receive Audio Setting ...............................................245
C. Transmit Audio Setting..............................................246
JUMPER FUNCTIONS AND LOCATIONS..............................................247
COMMAND SUMMARY...........................................................................250

MFJ-1270C/1274C MANUAL TABLE OF CONTENTS
viii

MFJ-1270C/1274C MANUAL INTRODUCTION
Page 1
INTRODUCTION
Thank you for purchasing the MFJ TNC Packet Data controller.
The MFJ TNC interfaces your radio with any personal computer that has an RS-
232 or TTL level Serial Port and a terminal program. While most
communications programs will work, MFJ recommends the use of MFJ Starter
Pack for those who have IBM or compatible, Macintosh, Amiga or Commodore
C64/128 computers. With an IBM or compatible computer, the MFJ Multicom
terminal program gives you added feature like VGA packet picture transfer
(IBM & compatible version) that a standard terminal program just can not offer.
This compact versatile controller employs the genuine TAPR TNC 2 AX.25
protocol packet firmware. Special firmware like ROSE, NETROM, TheNet are
compatible with the MFJ TNC.
In addition, the advanced new DCD circuit in the MFJ TNC has been optimized
for HF packet. It can be adjusted to ignore background noise while still being
able to respond to a valid data carrier. The new "packet collision prevention"
features -- Prioritized Acknowledgments and Slottime are installed. This new
technology helps prevent many packet collisions inherent in the current packet
protocol.
The MFJ TNC offers the most versatile mailbox available when compared to the
mailbox in other controllers. This mailbox allows dedicated mailbox callsign so
that the mailbox stays on while you operate packet. Other features like auto
forward or reverse forward mail to and from other BBS, remote sysop access,
sysop paging, mailbox ctext, chat mode and a "has mail" LED indicator. The
MFJ TNC has an 8K bytes memory mailbox. Mailbox memory is user
expandable to 32K, 128K or 512K by simply replacing the mailbox memory IC.
If you purchased the MFJ-1274C, you also get MFJ's 20- segment, 10 Hz
Precision Tuning Indicator that makes tuning simple for HF Packet.
The EPROM containing the MFJ TNC firmware is 256K bits. It is expandable
to 512K bit or 1 Megabits giving the MFJ TNC a lot of room to grow in.
A speaker jack lets you plug in a speaker and monitor both transmit and receive
audio. Speaker output also provides packet connect signal alarm.

MFJ-1270C/1274C MANUAL INTRODUCTION
Page 2
A 20-pin header provided for the MFJ TNC to operate packet at 2400 or 9600
baud packet by simply pluging in an optional modem board. The MFJ-1270CT
and the MFJ-1274CT already has a 2400 modem installed. If your MFJ TNC
does not have the 2400 modem installed, it can be purchased separately (MFJ-
2400) and installed by you. With the 2400 modem installed, your MFJ TNC can
operate 300, 1200 and 2400 packet. You may also purchased the MFJ-9600
modem board that allows the MFJ TNC to operate at 9600 baud packet.
Items supplied with MFJ TNC package
1. One MFJ TNC Packet controller.
2. One AC adapter power supply for 110V AC. 240V AC adapter supplied for
MFJ-1270CX or MFJ-1274CX (export model for country which operate on 220-
240V AC).
3. One open end radio port cable with 5-pin DIN male connectors.
4. One 8-pin connector for the TTL port.
5. One TNC system Instruction Manual.
6. One TNC Fast-Start Manual.
MFJ also has accessory items available for the MFJ TNC. A list of these items
follows on the next page.

MFJ-1270C/1274C MANUAL INTRODUCTION
Page 3
Optional items available for the MFJ TNC
Model No Description
MFJ-1289 Advanced Starter pack for IBM & compatibles
MFJ-1282 Starter pack for Commodore C64/128
MFJ-1287 Starter pack for Macintosh
MFJ-1290 Starter pack for Amiga
MFJ-1272B MFJ TNC to Microphone switch box
MFJ-5024 Radio connecting cable for Icom/Yaesu/RS HTs
MFJ-5026 Radio connecting cable for Kenwood HTs
MFJ-5080 Radio connecting cable for Yaesu 8-pin radio
MFJ-5084 Radio connecting cable for ICOM 8-pin radio
MFJ-5086 Radio connecting cable for Kenwood 8-pin radio
MFJ-280 Monitor speaker for transmit/receiver audio
MFJ-40E Packet encryption EPROM
MFJ-43 TNC Real time clock, keeps your TNC on-time
MFJ-45A 32K RAM IC for additional mailbox memory
MFJ-45B 128K RAM IC for additional mailbox memory
MFJ-45C 512K RAM IC for additonal mailbox memory
MFJ-2400 2400 bps internal modem for packet
MFJ-9600 9600 baud internal modem for packet
The above items are available from MFJ dealers or directly from MFJ
Enterprises, Inc.

MFJ-1270C/1274C COMPUTER INTERFACING
Page 4
COMPUTER INTERFACING
You are now ready to attach your MFJ TNC to your station computer or
terminal. Throughout this manual we will use the term "computer" to refer to
the computer or terminal you use to communicate with your MFJ TNC .
The MFJ TNC communicates with your computer through a serial port using
signals corresponding to a standard called RS-232C. Why an RS-232C
interface? Nearly every computer in production today either incorporates an RS-
232C style serial port as a standard feature, or has one available as an optional
accessory, either from the computer manufacturer or from a manufacturer of
computer accessories. In addition to the RS-232C port, the MFJ TNC has a
built- in TTL port to allow interfacing with computers which need TTL signals
such as the Commodore C-64, C-128 or the VIC-20.
Computer program\, see Terminal program
In order to use the MFJ TNC with your computer, the computer must have an
RS-232C serial port, or a TTL serial port and a program to support the serial
or TTL port. The program will typically be called a modem, terminal emulator,
or communications program.
Since there are so many computers on the market today, it is impractical for this
chapter to provide detailed instructions for each computer. Detailed information
is given for some of the popular models available in the United States. Also
provided is general computer interfacing information.
MFJ Terminal Software Starter Packs
MFJ Enterprises, Inc. offers a Starter Pack for some of the most popular
computers. These Starter Packs contain a terminal program and a cable for
connecting the MFJ TNC to your computer. The Starter Packs available are
listed below and also on the following page:
MFJ-1282:Commodore VIC-20, C64, C128 on 5-1/4" diskette.
MFJ-1283: Commodore VIC-20, C64 on tape.

MFJ-1270C/1274C COMPUTER INTERFACING
Page 5
MFJ-1284: IBM PC & compatibles on 5-1/4" diskette.
(Supports 2-level FAX)
MFJ-1284M: IBM PC & compatibles on 3-1/2" diskette.
(Supports 2-level FAX)
MFJ-1287B: Macintosh, on 3-1/2" diskette.
(Supports 2-level FAX)
MFJ-1290: Amiga on 3-1/2" diskette.
(Supports 2-level FAX)
Computer Interfacing with MFJ Starter Packs
If you are using one of the MFJ Starter Packs, you should use the cable provided
to connect the MFJ TNC and your computer. Follow the instruction manual
provided with the Starter Pack to operate the terminal program and to connect
the MFJ TNC to your computer. After connecting the MFJ TNC to your
computer you can then proceed to the "Computer Baud Rate" section in this
chapter to continue installing the MFJ TNC .
Computer Interface without MFJ Starter Pack
If you are not using a MFJ Starter Packs you should follow the instruction in this
chapter for computer interfacing.
Serial Port Signals
The serial port connector on your MFJ TNC is on the rear panel and is marked
"SERIAL." There are several signals available at this connector. You won't
need all of them for standard normal operation. For some special applications,
such as binary file transfers or some Bulletin Board operations, you may want to
use more of them. In that case, see MFJ TNC Serial Port Pin Functions in
this chapter.
The pins on the serial port connector of the MFJ TNC that must be connected
are shown in Table 2-1. Note that the MFJ TNC connects to a computer exactly
as if the MFJ TNC were a standard RS-232C modem. If you have successfully
used your computer with a telephone modem, hook it up to the MFJ TNC in the
same way. Use whatever program you ordinarily use to communicate with the
modem.

MFJ-1270C/1274C COMPUTER INTERFACING
Page 6
The basic serial port signals reauired by the TNC for normal operation are listed
below in Table 2-1.
Pin Signal Name Description
2 Transmit Data
Serial data from your computer to the MFJ TNC
3 Receive Data Serial data from the MFJ TNC to your computer
7 Signal Ground The common ground for both data lines.
Table 2-1. Serial port signals required by MFJ TNC .
If your computer is listed below in Table 2-2, refer to the specific information in
the following sections to connect your MFJ TNC to your computer.
Manufacturer Model
Apple Macintosh (tm)
Apple II,II+,IIe,II-gs(tm)
Commodore VIC-20 (tm)
C-64 (tm)
C-128 (tm)
IBM PCjr, PC-XT, PC-AT, 386/486
most PC compatibles
Radio Shack Color Computer (tm)
PC Compatiables
Amiga 500, 3000
NEC 8201
Table 2-2. Computers with specific serial interfacing instructions.
Many computers require a serial port adapter card. These cards incorporate the
circuitry necessary to add an RS-232C port to the computer. Some popular
models in this category are the Apple II series, the IBM Personal Computer,
many Radio Shack computers, and the Sanyo MBC-55X series. If you have one
of these computers with an "add-in" serial port, or if you have another computer
we haven't mentioned, you should skip to one of the sections on "other
computers." If your computer has a 25-pin RS-232C serial port, refer to the

MFJ-1270C/1274C COMPUTER INTERFACING
Page 7
section on Other Computers with 25-pin RS-232C Ports. Otherwise refer to the
section Other Computers with Nonstandard Serial Ports.
Some computers have no serial port and no adapter is commercially available.
Such computers are not suitable for use with the MFJ TNC.
Computers with Specific Serial Interfaces
Apple Macintosh
The Macintosh serial port is an RS-422 compatible port, but it will work fine
with the RS-232C serial port on your MFJ TNC .
MFJ Enterprises, Inc. offers an optional Starter Pack for the Macintosh. It can be
purchased from MFJ Enterprises, Inc. or any MFJ dealer. The Starter Pack
includes an interface cable for connecting the MFJ TNC to the Macintosh and a
terminal program. The Starter Pack for Macintosh is MFJ-1287. If you wish to
use your own cable, you will need a cable wired as shown in Fig. 2-1.
Macintosh MFJ TNC Macintosh MFJ TNC
8 pin DB-25P DB-9P DB-25P
1 (HSKO) 4 1 1
2 (HSKI) 5 5 2
3 (TXD-) 2 9 3
4 (GND) 7 3 7
5 (RXD-) 3 7 8
6 (TXD+) N/C 6 4
7 (GPi) 8
8 (RXD+) 7
Shield 1
Macintosh To MFJ TNC Cable Wiring
Fig. 2-1. Serial port wiring for Apple Macintosh.
Note that pin 1 of the DP-9P connector is not connected inside the Macintosh or
the MFJ TNC . If you use a shielded serial cable, which we recommend, connect
both pin 1s to the shield and connect pin 1 of the MFJ TNC serial connector to

MFJ-1270C/1274C COMPUTER INTERFACING
Page 8
digital ground on the MFJ TNC circuit board. A printed circuit board pad is
provided for this purpose near pin 1 of the serial connector.
Commodore C64, C128 and VIC-20
The MFJ TNC has a built-in TTL-level port for interfacing with the
Commodore C64, C128 or the VIC-20 computers. You do not need a RS-232C
converter to interface with the MFJ TNC.
An optional Starter Pack for the C-64, C-128 or the VIC-20 can be purchased
from MFJ Enterprises, Inc. or from any MFJ dealer. The Starter Pack includes
an interface cable from the MFJ TNC TTL port to the user I/O port on the
Commodore computer. A terminal program is also included. To order, specify
MFJ-1282 for software on disk or MFJ-1283 for software on tape.
If you wish to construct your own cable, the information is as follows:
MFJ TNC
J-5 Pin#
Mnemonic Name C-64/128*,
VIC-20 Pin#
1 RXD Receive Data B,C
2 DCD Data Carrier Detected H
3 GND Ground(Frame & Signal) N
4 RTS Ready To Send E
5 TXD Transmit Data M
6 DSR Data Set Ready L
7 CTS Clear To Send K
Fig. 2-2A TTL port wiring for VIC-20, C64 and C128
*C-128 is used in the C-64 mode for these connections.
**Pin E is not needed when using terminal program referred to in this
chapter for the Commodore computers.
The pin connections for the TTL port (J-5) are numbered from left to right as
you look at the back of the MFJ TNC . All of these connections are not
necessarily used by your terminal program. The MFJ TNC needs RXD, TXD
and GND connected. Programs which utilize file transfer and printer routines
will probably use RTS and CTS as well. Consult your software documentation.

MFJ-1270C/1274C COMPUTER INTERFACING
Page 9
IBM PCjr
The PCjr uses standard RS-232C voltage levels for its serial interface; however,
the connector used is non-standard and not readily available from electronic
supply dealers. Pinout information for this connector is given in the IBM PCjr
Technical Reference Manual.
IBM dealers sell the "IBM PCjr Adapter Cable for Serial Devices" for
converting the connector on PCjr to a standard RS-232C terminal connector.
This cable attaches directly between the MFJ TNC and the PCjr. It is only
about 3 inches long, however, so you may want to obtain a male-to- female RS-
232C extension cable, which should be readily available.
Radio Shack Color Computer
The Color Computer series (except for the Micro Color Computer) uses a 4-pin
DIN-style connector for its serial interface. Wire a cable as shown in Fig. 2-2 to
interface your MFJ TNC to a Color Computer. All necessary parts should be
available from Radio Shack dealers.
Color Computer DB-25P
4 2
2 3
3 7
Fig. 2-2
Serial port wiring for Radio Shack
Radio Shack Model 100/102 and NEC 8201
These computers have built-in standard RS-232C serial ports that are compatible
with the MFJ TNC . You will need a standard male-to-male RS-232C extension
cable to connect the computer to the MFJ TNC .
IBM PC/XT/AT/386/486 and compatibles Computer

MFJ-1270C/1274C COMPUTER INTERFACING
Page 10
If your computer is a IBM or compatible, you should have a serial port with
standard DB-25 or DB-9 pin connector. You may used a standard IBM serial
modem cable with the correct gender on each end of the cable.
MFJ Enterprises, Inc. offers optional Starter Pack (MFJ- 1284) for the IBM or
compatible computers. The Starter Pack is supplied with the computer
connecting cable (DB-25 male to DB-25 female) for connecting your MFJ TNC
For other computers with a 25-pin RS-232C port, you should consult your
computer manual or accessory manual to see which pins it uses to send and
receive data on, as well as which pin is used for signal common. Follow the
computer manufacturer's recommendations for connecting the serial port to a
modem. You may also find the technical information in this section useful.
Your MFJ TNC is configured as Data Communications Equipment (DCE), the
technical term for an RS-232C modem. Most computers are configured as Data
Terminal Equipment (DTE). If this is the case for your computer, you will
probably be able to simply wire pin 2 of the MFJ TNC connector to pin 2 of
your computer's RS-232C port, pin 3 to pin 3 and pin 7 to pin 7. You can
provide these connections with a standard 3- wire male-to-female or male-to-
male RS-232C extension cable, depending on whether your computer has a
DB25S or DB25P connector.
If your computer is configured as DCE, you will have to wire pin 2 of your MFJ
TNC to pin 3 of the computer connector, and pin 2 of the computer connector to
pin 3 of your MFJ TNC . Pin 7 of the computer connector will still connect to
pin 7 of your MFJ TNC serial port. Some computers may require that pin 5 of
the computer serial port connector be connected to an appropriate signal. Others
may require connections for pin 8 and pin 20. You can use the computer's
output signals on pins 4 and 6 as shown in Fig. 2-3.
MFJ TNC
RS-232c
Computer
2 2
3 3
7 7
4
5
6
8

MFJ-1270C/1274C COMPUTER INTERFACING
Page 11
20
Fig. 2-3. Serial port wiring with jumpers for auxiliary signals.