____ _ __ __ _
| __ ) __ _ ___(_) ___ | \/ | ___ __| | ___ _ __ ___
| _ \ / _` / __| |/ __| | |\/| |/ _ \ / _` |/ _ \ '_ ` _ \
| |_) | (_| \__ \ | (__ | | | | (_) | (_| | __/ | | | | |
|____/ \__,_|___/_|\___| |_| |_|\___/ \__,_|\___|_| |_| |_|
____ _
/ ___|___ _ __ ___ _ __ ___ __ _ _ __ __| |___
| | / _ \| '_ ` _ \| '_ ` _ \ / _` | '_ \ / _` / __|
| |__| (_) | | | | | | | | | | | (_| | | | | (_| \__ \
\____\___/|_| |_| |_|_| |_| |_|\__,_|_| |_|\__,_|___/
INTRODUCTION:
-------------
Modem,n: Short for MOdulator-DEModulator. A device which is connected between
a digital equipment (like computer) and an analog transmission medium
(like telephone line). It converts digital signals into analog
signals and vice-versa.
Digital Analog Analog Digital
Data Signal Signal Data
: : : :
: : : :
: : : :
ÚÄÄÄÄ¿ : : : : ÚÄÄÄÄ¿
³ ³ : : // : : ³ ³
ÀÄÄÄÄÙ v ÚÄÂÄ¿ v //__ v ÚÄÂÄ¿ v ÀÄÄÄÄÙ
ÛÛÛÛÛÛÛÛ°======°³ ³ ÆÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ/__ /ÍÍÍÍÍÍÍÍÍÍÍÍ͵ ³ ³°=======°ÛÛÛÛÛÛÛÛ
^ ÀÄÁÄÙ ^ // ^ ÀÄÁÄÙ ^
Computer 1 | Modem 1 | // | Modem 2 | Computer 2
| | | |
| | | |
| | | |
Local Link Telephone Link, Telephone Link, Local Link
RS-232C,etc. Radio,etc. Radio,etc. RS-232C,etc.
FIG 1
A modem, at a basic level, converts a digital signal (typically 1 and 0
represented by +5 volts and 0 volts (also +12 volts and -12 volts in RS-232C
protocol) into a analog signal in the range which a telephone connection can
carry.
OK! enough of the theory stuff. How about some practical stuff...namely,
how to get your modem up and running...eh!?
Fine! first thing we look into is how to connect the (stupid) modem to the
computer. Now modems come in two types:
* EXTERNAL: these modems come as cute boxes with their own power supply
(adapter). You use a serial cable to connect these to your computer
through one of your serial (comm or RS-232C ports). Obviously you would
need a serial cable to connect these two things together.
* INTERNAL: these are modems on cards which plug into one of the slots
in your computer. You don't have to bother about the connecting cable
nor any physical port connection being used up.
These commands have to be issued from within your communication package.
When you invoke the communication. program it will open and initialise your serial
port (to which the modem is connected) provided the setup is correct.
To check, type: AT
This should display OK or 0. Anything else or no response means things are
not "OK". You have to check out the program's setup.
In general:
* Set the serial port to which your modem is physically connected.
In case of an internal modem check if it is properly configured (normally
you might have to set dip switches located on the card).
* Set the serial port speed according to the following list:
110,300,600,1200,4800,9600,14400,19200,28800,38400,57600,115200
Select a value which is one step more than your modem speed. For example
if you have a 14.4KBps modem then set the serial port speed as 19200.
* Set parity as no, wordlength as 8 and stopbit as 1
* Set terminal emulation as Ansi or VT100
HOW TO MANUALLY DIAL IN:
Follow this sequence. It should work for most of the modems.
(Type) AT * check if everything is ok
(Response) OK or 0 * no response or anything else see above
(T) AT&FV1M1L3 * set up the modem (actually you have to do
(R) OK this only once every session).
(T) ATDPxxxxxx * dial the number, xxxxx...is the number to be
dialled.
* now you will hear clicks or beeps from the modem
as it dials, followed by all the normal sounds
just like when you are making a normal voice call.
Once the modem at the other end picks up the
call, you will hear a high pitched warbling
whistle. This is the handshaking phase. Once
the connection is made all sounds will cease.
And the sign-on screen from the remote machine
will be displayed on your screen. Just follow
the instructions/menus displayed...
In case you want to re-try the same number (the remote modem was busy)
then type in the following:
(T) A/ * this will repeat the last command i.e. the
number which you had previously dialled. No
need to press after the command.
After you have finished then either the remote hosts breaks the connection
or you can break it using the following command:
(T) ATH0
(R) OK
HOW TO ANSWER AN INCOMING DATA CALL:
(R) RING or 2 * modem indicates that an incoming call has been
detected.
(T) ATA * pick up the call.
Some Basic Modem commands (Hayes AT compatible)
-----------------------------------------------
AT -- Attention command. This precedes most of the modem commands.
Dialling:
---------
ATDPnnnnnnnnn -- Pulse Dialling; nnnnnnnn is the ph. number to be dialled
ATDTnnnnnnnnn -- Tone Dialling; nnnnnnnn is the ph. number to be dialled
ATA -- answer an incoming call
A/ -- repeating the last command
Setup:
------
AT&F -- Load the factory default settings
ATZ -- Reset & retrieve a stored configuration
AT&V -- Display the stored configuration(s)
ATS10=xxx -- Set the carrier loss time. xxx=1 to 255 "10th of a second"s.
ATS7=xxx -- Set remote carrier wait time. xxx=1 to 255 seconds.
ATV1 -- Set word response from the modem
ATX4 -- All responses/dial tone/busy signal detection enabled
ATLx -- Set modem speaker volume. x=0 to 3
ATHx -- x=0 Hang up x=1 make busy
ATMx -- x=0 Speaker off x=1 Speaker on until carrier detected
x=2 Speaker always on x=3 Speaker on until carrier detected
& off while Dialling.
If and when you feel confident or adventurous then check your modem manual
for further commands and setup information.
CONNECTING YOUR MODEM TO YOUR COMPUTER
======================================
Internal Modem:
* Run a diagnostic program (like MSD) to see which port - IRQs & ADDRESSes
are free.
* Set one of the free IRQ/ADDRESS on the modem card (by dip switch or in
software, as the case maybe). RTFM.
* Open the computer. Locate a free slot & insert the card in the slot.
Obviously the computer should be off :)
* Connect the telephone line.
External Modem:
* You will need a free serial port & a serial cable.
If you need to make your own cable or check the existing cable then see
below:
If the computer serial port is 25 pin & the modem port is 25 pin then
the serial is straight through cable, that is, each pin of one connector
is connected to the corresponding pin of the other connector.
DIAGRAM -- yet to be drawn & included...:(
25 pin to 25 pin
9 pin to 25 pin
Modems mostly have a 25 pin connector
Û T I P ßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßÛ
Û Û
Û If the AC adaptor provided with the modem is bad or goes bad later on Û
Û then buy a regular AC to DC adaptor whose output voltage rating is about Û
Û 3-4 volts higher than your modem voltage rating. e.g. if modem voltage Û
Û (will be written on the modem or in the manual) = 15 Volts then buy an Û
Û adaptor of 18 volts. Û
Û Open this adaptor and remove the filter circuit (diodes, capacitors,etc) Û
Û and directly connect the output cable to the transformer secondary. Û
Û Û
Û Û
Û Û
Û ÛÝÝÛÞÞ ÚÄÄÄÄÄÄÄÄ¿ Û
Û ÉÍÍÍÛÝÝÛÞÞÍÍÍ» ³ ÛÛ ßßß ³ Û
Û AC Input Í Í Í Í Í Í Í Í¹ ø ÛÝÝÛÞÞ ßÄ×ÄÄÄíÄÄÄÄÄ´ ÛÛ ßßßÃÄÄÄÄ Û
Û 220 VAC º ÛÝÝÛÞÞ º \ ³ ÜÜÜ Ýܳ DC Output Û
Û From AC Í Í Í Í Í Í Í Í¹ ø ÛÝÝÛÞÞ ÜÄ×ÄÄÄíÄ\ÄÄÄ´ÜÜÜÜ ÝÛÃÄÄÄÄ Û
Û mains plug ÈÍÍÍÛÝÝÛÞÞÍÍͼ ^\ \ ÀÄÄÄÄÄÄÄÄÙ Û
Û ÛÝÝÛÞÞ : \ \ Rectifier Û
Û Step Down : \ \ Circuit Û
Û Transformer : \ \ Board Û
Û : \ \ Û
Û : \ \ Û
Û : \ \ Û
Û : \ \_ _ _ _ AC Output Jack Û
Û : \_ _ _ _ _ To the modem Û
Û : Û
Û ÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜÜ Û
Û ÛDisconnect the rectifier boardÛ Û
Û Ûat the points marked í & í andÛ Û
Û Ûdirectly connect to the outputÛ Û
Û Ûjack. Û Û
Û ßßßßßßßßßßßßßßßßßßßßßßßßßßßßßß Û
Û Û
Û Û
Û FIG 2: Modifying a commercially available AC to DC adaptor for Û
Û Modem use. Û
Û Û
ßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßß
Û T I P ßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßÛ
Û Û
Û There is an excellent shareware/freeware utility, CHKMODEM.EXE, for Û
Û beginners. This utility is fairly automatic; needs no inputs from you. Û
Û After you have connected your modem, you can use this to check Û
Û the modem (COM port, address, speed). You will need these values to setup Û
Û your communication program. You can download CHKMODEM.EXE from most of Û
Û your local BBSes. Û
Û Û
Û USING CHKMODEM.EXE Û
Û __________________ Û
Û_______STEP 1________ Û
Û Run CHKMODEM.EXE to detect modem and port settings Û
Û If your modem is correctly connected and there is no hardware problem Û
Û then the final message displayed by CHKMODEM.EXE would be something Û
Û similar to the following : Û
Û Û
Û ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ» Û
Û º Modem Found on SCAN# 2 @ ADDR = 2F8 INT = 3 MinBaud = 300 MaxBaud = 9600º Û
Û º Responds with - CD LOW - CD HIGH - DTR HIGH - HandShake = NONE º Û
Û ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ Û
Û Û
Û -> SCAN# 2 means that your serial (RS-232) port number is 2 Û
Û -> ADDR is the address of the port Û
Û -> INT is the interrupt number for the port Û
Û -> MaxBaud means the maximum speed (of the serial port) at which the Û
Û modem responds. This may be different from the external speed (the Û
Û speed at which the modem communicates with another modem over the Û
Û telephone lines). Û
Û Û
Û_______STEP 2________ Û
Û Open up your communication program and go to the setup options and fill Û
Û in the values displayed by CHKMODEM.EXE. Û
Û Û
Û The following are the entries which you might have to fill in: Û
Û Û
Û ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ» Û
Û º º Û
Û º port=2 Set this to the value (SCAN#) found in STEP 1 º Û
Û º º Û
Û º speed=9600 Put the MaxBaud value from STEP 1 º Û
Û º º Û
Û º irq=3 Put the INT value from STEP 1 º Û
Û º º Û
Û º addr=2F8 Put the ADDR value from STEP 1 º Û
Û º º Û
Û ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ Û
Û Û
Û Û
ßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßßß
|
