ELSA MicroLink 56k Internet User manual

ELSA MicroLink
TM
56k Internet
User Manual

No. 20833/0299
Copyright © 1999 ELSA AG, Aachen (Germany)
Whiletheinformationinthismanualhasbeencompiledwithgreatcare,itmaynotbedeemedanassur-
ance of product characteristics. ELSA shall be liable only to the degree specified in the terms of sale
and delivery.
Thereproductionanddistributionofthedocumentationandsoftwaresuppliedwiththisproductandthe
use of its contents is subject to written authorization from ELSA.
ELSAisDINENISO9001certified. TheaccreditedTÜVCERTcertificationauthorityhasconfirmedELSA
conformity to the worldwide ISO 9001 standard in certificate number 09 100 5069, issued on June 15,
1998.
Trademarks
Windows®, Windows NT®and Microsoft®are registered trademarks of Microsoft, Corp.
Allothernamesmentionedmaybetrademarksorregisteredtrademarksoftheirrespectiveowners. The
ELSA logo is a registered trademark of ELSA AG.
Subject to change without notice. No liability for technical errors or omissions.
ELSA AG ELSA, Inc.
Sonnenweg 11 2231 Calle De Luna
52070 Aachen Santa Clara, CA 95054
Germany USA
www.elsa.de www.elsa.com
Aachen, February 1999

Preface
Thank you for placing your trust in this ELSA product.
With the
ELSA MicroLink 56k Internet you have chosen a modem which enables
youtomake use of the new 56k technology. The
ELSA MicroLink 56kInternet sup-
ports the AT command set in compliance with V.250.
Exacting manufacturing standards and stringent quality control are the basis for
high product standards and consistent quality to ensure your fullest satisfaction
with this modem.
About this manual
Thismanualwillinformyouaboutall aspectsof your ELSA MicroLink56k Internet .
It also contains an overview of the AT command set.
Online documentation
The modem CD contains extensive electronic documentation in addition to the
printed handbooks. This provides information on topics such as the installation of
accesssoftware,theonlineservicesandothersupportnotes.Thisinformation has
been stored in PDF format. A browser (e.g. Netscape Navigator or Microsoft Inter-
netExplorer)isrequiredforreadingandprintingHTMLfiles.TheACROBATReader
programisrequiredtoreadandprintPDFfiles.Itcanalsobefoundontheincluded
CD and may be installed using the CD setup program.
To read the online documentation, proceed as follows:
aInsert the included ELSA modem CD in your CD drive. The CD setup will start
automatically under Windows 95, Windows 98 and Windows NT 4.0. If you
are using a different operating system, please start the CD setup program
(CDSETUP.EXE) on the CD.
bIn the CD setup program, select Installation of:, mark the option ONLINE
documentation (requires ACROBAT Reader), and clickDisplay.

Contents
ELSA MicroLink 56k Internet
IV
Contents
Contents ........................................................................................................................IV
Introduction ....................................................................................................................1
Your
ELSA MicroLink 56k Internet ’s vocabulary..................................................... 1
What do I need for
ELSA-COMMUNICATE! Lite ?................................................. 3
Package contents.................................................................................................... 3
CE conformity.......................................................................................................... 4
Control commands ........................................................................................................5
Entering and executing AT commands................................................................... 5
Escape command............................................................................................... 5
Bit-oriented registers.............................................................................................. 6
Modifying bit-oriented registers........................................................................ 6
Overview of AT command set and registers.......................................................... 6
Basic control features........................................................................................ 7
Extended control features.................................................................................. 7
Appendix .........................................................................................................................9
Brief overview of the AT command set.................................................................. 9
Status display and troubleshooting...................................................................... 12
Technical data....................................................................................................... 13
Characteristics of the modem.......................................................................... 13
Frequently asked questions and answers............................................................ 14
General topics.................................................................................................. 14
WinFax............................................................................................................. 16
Warranty conditions............................................................................................. 17
Glossary ........................................................................................................................19
Index ..............................................................................................................................23

Contents
ELSA MicroLink 56k Internet
V

Introduction
ELSA MicroLink 56k Internet
1
Introduction
The ELSA MicroLink 56k Internet is a desktop device that is contained by a flat, stable
plastic casing. The hardware installation is fast and user-friendly thanks to plug&play
support (see Installation Guide).
The included
ELSA-COMMUNICATE! Lite software suite is a communications program
which provides you with the most important data communications applications in a con-
venient, easy-to-use package.
ELSA-COMMUNICATE!Lite providesthefollowingfeaturesinconjunctionwithyourmo-
dem:
Ktelephone answering machine
Kfax
KInternet e-mail
Kaddress book (e.g. fax and telephone numbers)
Kintegrated terminal program
It is possible to upgrade to the full version of
ELSA-COMMUNICATE! PRO .
Your
ELSA MicroLink 56k Internet
’s vocabulary
Thefollowingis an outline of the essential technical features ofthemodemtoprovide a
quick overview of its functionality:
KTransmission modes –
ELSA MicroLink56kInternet supports thefollowingtrans-
mission modes and speeds:
– V.90: 28,000 to 56,000 bps (receiving bit rate only)
– K56flex: 28,000 to 56,000 bps (receiving bit rate only)
– V.34: 2400 to 33,600 bps duplex
– V.32bis: 4800 to 14,400 bps duplex
– V.32: 4800 to 9600 bps duplex
– V.22bis: 1200 to 2400 bps duplex
– V.23: 1200 bps half-duplex
– 75/1200 bps duplex
– 1200 bps half-duplex
– Bell 212A: 1200 bps duplex
– V.21: 300 bps duplex
– Bell 103: 300 bps duplex
KV.90 –International ITU standard for data communications with 56k modems.

Introduction
ELSA MicroLink 56k Internet
2
KFax operation – The
ELSA MicroLink 56k Internet supports fax transmission and
reception at speeds of 2400 to 14,400 bps in addition to the modem operating
modes. The Class 1, Class 1.0, Class 2 and Class 2.0 fax command sets permit the
use of any standard fax software, as well as the Windows 95, Windows 98,
Windows NT or Windows for Workgroups e-mail functions.
KFax polling – Themodem supports fax polling. Theunitcanbe used for fax polling
or the operation of a polling system together with suitable fax software.
KAnswering machine – With the included voice software, you can use the
ELSA MicroLink 56k Internet as an answering machine.
KAccesscontrol,callback and remote configuration–Accesscontrolservesto
protect your modem from operation or configuration by unauthorized persons. By
means of a password, the so-called supervisor password, certain modem functions
can be locked. Five access flags can be used to define which modem functions are
locked.
– Thecallbackfunctionautomaticallyreturnscallsplacedtothemodem.Atotalof
19 callback numbers and their associated passwords can be stored.
– Theremote configuration function allows you to configure your modemfromany
location you are calling from and can be combined with the automatic callback
function.
KError correction –The MNP4 and V.42 error correction protocols implemented in
the modems allow error-corrected data transmission even with poor quality tele-
phone connections.
ELSA MicroLink 56k Internet with MNP4 or V.42 can establish
reliable, error-free connections to other, similarly equipped modems.
KData compression –
ELSA MicroLink 56k Internet uses the MNP5 and V.42bis
datacompressionmethods.UsingMNP5,thetransferratescanbedoubled,oreven
quadrupled in the case of V.42bis.
KATcommandset–TheATcommandsetinaccordancewithV.250isusedforcom-
munications with the
ELSA MicroLink 56k Internet .
KFlash-ROM technology – Firmware updates can be performed quickly and easily
usingflashROMtechnology.Thisprovidesaconvenientwaytoequipyourunitwith
future options.
KGuaranteed – two-year warranty on
ELSA MicroLink 56k Internet
KProtected – The
ELSA MicroLink 56k Internet satisfies the CE requirements.

Introduction
ELSA MicroLink 56k Internet
3
What do I need for
ELSA-COMMUNICATE! Lite
?
The following minimum requirements must be fulfilled for the use of the modem with
ELSA-COMMUNICATE! Lite :
KComputer: A PC with at least a 486 processor is recommended. Approx. 100 MB
free disk space is required for a complete installation. After installation, the
ELSA-
COMMUNICATE! Lite
takes up about 25 MB disk space.
KCD-ROM: CD-ROM drive
KRAM: a minimum of 16 MB
KModem:
ELSA MicroLink 56k Internet
KOperating system: Microsoft Windows 95, Windows 98 or Windows NT
KActive speakers: Werecommend theuse of activespeakers inconjunctionwith a
sound card.
KHeadsetorMicrophone:aheadsetormicrophonecanonlybeusedinconjunction
with a sound card.
Package contents
Pleaseensurethatthedeliveryiscompletebeforebeginningwiththeinstallationofyour
modem:
K
ELSA MicroLink 56k Internet
KPower adapter
KTelephone line connection cable
KModem connector cable (V.24/RS232 cable)
KCD-ROM with application software
KDocumentation: Installation Guide, User Manual (as PDF file)
ELSA reserves the right to change the package contents without prior notice.

Introduction
ELSA MicroLink 56k Internet
4
CE conformity
The CE seal indicates compliance with rules laid down by the European Community on
April29, 1991 for thealignmentand mutual recognitionofthe member states' lawscon-
cerning telecommunications devices.
The
ELSA MicroLink 56k Internet has such a CE seal, guaranteeing:
KImmunity to interference according to EN 50082
Electromagneticcompatibility;Genericimmunitystandard;Part1:Residential,com-
mercial and light industry
KLow radio emission according to EN 55022
Electromagnetic compatibility of information technology and telecommunications
equipment
KElectrical safety according to EN 60950
Safety of information technology equipment including electrical business equip-
ment

Control commands
ELSA MicroLink 56k Internet
5
Control commands
The so-called AT command set established itself as the worldwide standard for modem
control command syntax (AT = command prefix Attention). The implementation of this
command set was left up to the individual manufacturer. The V.250 command set is a
standard for the AT command set. This is recommended by Microsoft for the PC98 spe-
cification and is a requirement of the PC99 specification.
Your
ELSA MicroLink 56k Internet is a state-of-the-art modem equipped for the V.250
command set.
AterminalprogramisrequiredtoenterATcommandsviaaPC(e.g.
ELSA-COMMUNICA-
TE! Lite
).
Entering and executing AT commands
After being switched on, the modem is in the command state. Commands can only be
accepted, interpreted and executed in this phase.
In the event that several commands are to be sent to the modem, these may be entered
individually,eachwithanATcommandprefixandaconcludingM. Itisalsopossible,
however, to enter these commands consecutively in a single command line after an in-
troductory AT and to conclude the line with an M.
Theindividualcommandsmaybeseparatedbyspacestoimprovetheoverview. Nofurt-
her characters may be entered once the end of the command line buffer has been rea-
ched. ThecommandlinecanthenonlybeeditedwithR(backspace)orexecutedwith
M.
Escape command
Usethecharacters -xand -ctoabortacommandlineorascreenoutput(e.g.
in case of displaying the register contents useAT%R).
Commands that must be specified with a parameter may also be entered without a pa-
rameter. Theabsenceofa parametercorresponds totheparameter0(e.g. ATI = ATI0).
After the successful establishment of a connection to the remote station, the modem
switches from the command phase to the transfer phase.
Transferphasemeans thataconnectiontoaremotedatastation (i.e.toanothermodem)
exists:Themodemisonline. Thisisthecasewithbothasuccessfulconnection(outgoing
call) and with the acceptance of an incoming call. The exchange of data between two
data stations can take place during this phase.
Arenewedtransitiontothecommandphaseandback,alsointhecaseofanexistingcon-
nection,ispossiblewiththeescapecommandandthecommandATO. Theescapecom-

Control commands
ELSA MicroLink 56k Internet
6
mand consists of a series of three escape characters (default setting: +++) and a valid
command line.
After the three escape characters have been entered, the modem is in the command
state. However, data transmission is interrupted only after the recognition of a valid
command line.
The escape character has nothing in common with the character Eof the ASCII cha-
racter set. It can be redefined in register S2.
Allcommands senttothe modemmustbegin withthe ASCII charactersAT orat (not va-
lid: At or aT) and must be concluded with M. A valid command line in an escape se-
quence is restricted to a maximum of 40 characters.
The command AT&F loads the firmware default parameter settings. If a connection
exists, this command is not executed.
Bit-oriented registers
Bit-oriented registers are primarily used to provide status information. Please note that
changing the value of a bit-mapped register can affect several functions at once! Great
cautionshouldthusbeappliedwhenchangingbit-orientedregisters! Tochangethecon-
figuration of your modem, you should use the AT commands instead. A complete des-
cription of the S registers can be found on the ELSA modem CD.
Modifying bit-oriented registers
Thefollowingexamplewillillustratethemodificationofthebit-orientedoptionsofare-
gister. To set the bit 6 of register S14, enter the commandATS14.6=1.
If you would like this value to be maintained after the modem adapter is switched off,
the new entry can be stored with the command AT*W.
Overview of AT command set and registers
In this brief overview, which is grouped according to topics, you find frequently needed
ATcommandsandregistersyoucanusetochangeyourmodemsettings. Acompletede-
scriptionoftheATcommandsetandregisterscanbefoundontheCDwhichcomeswith
the modem.
The 'Commands and registers' column lists AT commands and registers you can use to
change the basic settings of the modem. The 'More commands and registers' column
lists AT commands and registers for extended control of the modem.

Control commands
ELSA MicroLink 56k Internet
7
Basic control features
Extended control features
Configuration Commands and registers More commands and
registers
Basic initialization of the modem AT&F
Control of call establishment
(dialing) ATD, ATT, ATX AT$D, AT:D, S6, S7, S8, S14 (bit 6)
Callacceptance,takingoverofthe
line, hang up ATA, ATD, ATH, AT&D2, S0 AT-H, AT\T, S14.6, S28 (bit 7)
Transition between command and
transfer phase +++, ATO S2
Control of speaker and of call
signaling ATL, ATM, S54 (bit 0)
Read out modem information ATI, ATS, AT&V AT%R, AT\S, AT%V, S86
Control data compression AT+DS
Control error correction AT+ES
Control data flow monitoring AT+IFC S130
Control dial lock or dial delay S31 (bit 7)
Configuration Commands and registers More commands and
registers
Operation with saved initializati-
ons AT&V, AT&T, AT*W, AT&Y, ATZ S54
Operate with saved phone
numbers AT+ASTO
Protected access and callback AT$B, AT$Y, AT$S, AT$P, AT$R S35, S42, S43, S53
Remote configuration AT*E, AT*U, AT*X S34
Special control features
Control modem signal lines AT&C AT\D, AT&S
Control the effects of DTR AT&D AT$D, AT:D, S28 (bit 7)
Control modem answers ATE, ATQ, ATV, AT\V AT&D, AT-H, AT-M, AT*Q, S96
Control call tones AT&G
Control transfer method AT+MS
Control data format S28 (bit 0-1), S53
Control telephone-side speed AT+MS

Control commands
ELSA MicroLink 56k Internet
8

Appendix
ELSA MicroLink 56k Internet
9
Appendix
Brief overview of the AT command set
ThecompleteATcommandsetcanbefoundintheonlinedocumentationontheincluded
CD.
Command Description
A Answer incoming call
%A Fallback character in the negotiation phase
+A8E Control of the V.8 and V.8bis negotiation
+ASTO Saving speed-dial numbers
$B0
$B1
$B2
No callback
RING and CONNECT are displayed before the access procedure
RING and CONNECT are displayed after the access procedure
\C0
\C1
\C2
No data buffering in the negotiation phase
Data buffering in the negotiation phase
No data buffering, fallback character recognition (AT%A)
&C0
&C1 DCD is always active DCD follows the state of the carrier
$CS Query of the current modem settings
D Call establishment
$D0
$D1 Disables DTR dialing
Enables DTR dialing
&D0
&D1
&D2
&D3
Ignore DTR
Change to command state DTR ON ⇒OFF (ON ⇒ OFF)
Hang up if DTR ⇒OFF (ON ⇒ OFF)
Abort connection and reinitialize if DTR ⇒OFF ⇒
:D0
:D1 Modem does not go online if DTR OFF ⇒ON Modem goes online if DTR OFF ⇒ON
+DS Data compression method
E0
E1 Disable command echo Commands echoed
%E0
%E1 Automatic retrain off Enable automatic retrain
*E0
*E1 Remote configuration off
Remote configuration on
+EB Break signal handling
+EFCS FCS operating mode in V.42 mode
+ER Display of error correction method
+ES Selection of error correction method
+ESR Control of selective repeat function in V.42 mode

Appendix
ELSA MicroLink 56k Internet
10
+ETBM Buffer handling on aborted connection
&F Load default configuration
&G0
&G1
&G2
&G4
&G5
&G6
Calling tone on, no guard tone
Calling tone on, guard tone 550 Hz
Calling tone on, guard tone 1800 Hz
Calling tone off, no guard tone
Calling tone off, guard tone 550 Hz
Calling tone off, guard tone 1800 Hz
H0
H1 Go on-hook Go off-hook
-H0
-H1 Normal operation Dumb mode
I0
I1
I2
I3
I4
I6
I7
I9
Report product code in nnn format
Report checksum
Report checksum result
Display firmware version and date
Display of current parameters
Display product name
Report self-test result
Display plug&play information
L0
L1
L2
L3
Low speaker volume
Low volume
Medium speaker volume
High speaker volume
M0
M1
M2
M3
Speaker always off
Speaker on during call establishment
Speaker always on
Speaker on during waiting for answer tone
-M0
-M1 Plain text CONNECT messages dependent on AT\V Plain text CONNECT messages independent of AT\V
O0
O1 Transition to online status Return to online state with retrain
+MR Return modulation method and line bit rate
+MS Set modulation method
P Set pulse dialing
$P Enter and save user password and callback number
Q0
Q1
Q2
Enable modem result codes
Disable modem result codes
Messages off in answer mode
*Q0
*Q1 CONNECT message after invalid escape sequence No CONNECT message after invalid escape sequence
%R Display register contents
$R Display user password and parameters
S Set and read the internal register
\S Display the current configuration in verbose form
$S Set access flags
Command Description

Appendix
ELSA MicroLink 56k Internet
11
$S? Display current access flag setting
T Tone dialing method
&T0
&T1
&T3
&T4
&T5
&T6
End loopback mode
Activate local loopback
Activate loopback for remote modem
Activation of loopback by remote modem permitted
Activation of loopback by remote modem locked
Activate remote digital loopback
\T Inactivity timer
$T0
$T1 Trace mode off Trace mode on
*U Save current remote configuration
V0
V1 Messages in short form as a digit Messages in plain text
%V Display of firmware version
&V Display configuration profiles
\V0
\V1
\V2
\V8
No modified CONNECT messages
Identification of error-free connections
Identification of MNP and V.42(bis) connections
Identification of MNP, V.42 and V.42bis connections
&W0
&W1 Save extended configuration profile 0 Save extended configuration profile 1
*W0
*W1 Save extended configuration profile 0 Save extended configuration profile 1
X0
X1
X2
X3
X4
Ignore dial tone/ignore busy tone
Ignore dial tone/busy tone
Wait for dial tone/ignore busy tone
Ignore dial tone/evaluate busy tone
Wait for dial tone/evaluate busy tone
*X Exit remote configuration
&Y0
&Y1 Load configuration profile 0 at startup Use configuration profile 1 at startup
$Y Change supervisor password
Z0
Z1 Load configuration profile 0 Load configuration profile 1
. Setting and reading a bit in a register
Command Description

Appendix
ELSA MicroLink 56k Internet
12
Status display and troubleshooting
The LEDs on the front panel show the condition of the interface lines or the condition of
the modem.
1Data to modem
2Data from modem
3Computer operational
4Hardware handshake control line from modem
5Connection established
6Modem online (off hook)
7V.90 connection
8Modem power on

Appendix
ELSA MicroLink 56k Internet
13
Technical data
Users with specific technical interests should refer to this chapter for detailed informa-
tion on
ELSA MicroLink 56k Internet . All connections and their pin assignments are de-
scribed in detail.
Characteristics of the modem
ELSA MicroLink 56k Internet
Power supply 230 V/9VAC power adapter, TÜV-GS approved
Power consumption
(approx.) Transmission phase (online) 700 mA typ. Command phase (online) 350 mA typ.
Power consumption 9.9 VA typ.
Dimensions and design 168 x 35 x 130 mm (W x H x D), plastic housing
Ambient conditions 5..40°C
0..80%, non-condensing
Transfer protocols and
speeds 56,000..300 bps asynchronous, transmission and reception 33,600..300 bps asynchronous (V.90, K56flex, V.34, V.32bis, V.32, V.22bis, V.21, V.23,
V.80, Bell 212A and Bell 103)
Error correction V.42 and MNP Class 4
Data compression V.42bis and MNP Class 5
Command Set AT command set in accordance with V.250/V.25ter
Fax operation 14,400..2400 bps in accordance with V.17, V.33, V.29 and V.27ter; fax
command set,
TR-29.2 Class 2 (SP-2388), Class 2.0 (TIA/EIA-592), Class 2.1 (ITU-I.32),
Class 1 (TIA/EIA-578) and Class 1.0 (ITU-T-T.31)
Voice operation Voice command set in accordance with TIA/EIA IS 101 and Rockwell
Dialing method Dual-tone multifrequency dialing
External call Via flash function or digit
BPS ADJUST automatic in accordance with V.8 and V.100 (can be disabled)
Computer interface V.24/RS-232
CE conformity Tested in accordance with EN 50082/Part 1, EN 50081/Part 1, EN 61000-
4-2,3,4,6, ENV 50204, EN 55022, Class B, EN 60950
EU approval according to CTR21 + Advisory Notes EG 201 121

Appendix
ELSA MicroLink 56k Internet
14
Frequently asked questions and answers
General topics
How can I give AT commands to my modem?
To communicate with a modem via your PC, you need a communications software, also
called"terminalprogram" (e.g.
ELSA-COMMUNICATE!Lite ).Afterstarting thecommuni-
cationssoftware,youcanenterATcommandsintheterminalscreen.Theprogramsends
these commands to your modem via the serial interface of your PC.
What is the initialization string of the modem?
Thedefault setting of the modemisoptimally configured for accessingBBSs,onlineser-
vices and Internet providers. If you have changed the configuration and come across
problems with a BBS, you can restore the factory default settings with the AT&F com-
mand and save the configuration with AT*W.
My modem no longer accepts AT commands. Is it incorrectly configured or
faulty?
IfenteredATcommandsarenotdisplayedonthescreenandnotexecutedbythemodem,
this can have several possible reasons. You should check the following settings:
KIs your communications program set to the correct serial interface (COM port), i.e.
the one your modem is connected to?
KIs the DTE rate (serial port bit rate) of your communications program set to a value
within the speed range recognized by your modem?
KIfyourmodemconfigurationhasbeenchanged,trytoresetthemodemtothefactory
default configuration with the AT&F command (even if this command does not ap-
pearonthe screen). In the defaultstate,youshould be able to enter anAT which is
answered with OK by the modem.
I get a NO DIALTONE message from the modem after each dialing attempt and
cannot establish a connection. What can be the reason?
Youareprobablydialingfromanextensionofaprivatetelephoneexchange.Mostprivate
telephonesystemsrequireanescapedigit(e.g.0)tobedialedtogetthedialtoneofthe
main(external)line.Ifthisisthecase,dialoutusingthecommandATDT0W<number>.
The dialing parameter Wcauses the modem to wait for the continuous dial tone before
dialing the <number>.
Ifyou arecallinganother extension withinthe telephone system,nodial toneispresent.
Inthiscase,usethe dial commandATX3DT<number>, respectively. You can makethis
setting permanent with the ATX3*W command.

Appendix
ELSA MicroLink 56k Internet
15
Yourmodem cannot be used onaPBX which only permitsanoutsideline to be accessed
using the grounding key.
I'm dialing via a PBX, and although I get a dial tone and the remote station is
not busy, I constantly get a BUSY message? What's wrong?
In some cases the modem may regard the internal dial tone of a private telephone ex-
change as a busy tone. Disable the busy tone detection with the ATX0 command (in the
Netherlands: ATX2), and save this setting with AT*W. If you dial a busy line with this
setting, you will get a NO CARRIER message.
I frequently get CRC errors when uploading or downloading files to/from a
BBS; sometimes the connection is even lost. What is the reason?
CRC errors can have different reasons. One possible reason is an improper or missing
handshake method. To take advantage of data compression protocols, the DTE rate (i.e.
theserialportratedefinedinthecommunicationssoftware)shouldnormallybesethigh-
erthanthetelephoneside(DCE)rate(e.g.115,200bpsinstead).However,thisabsolutely
requires a handshake method for data flow control, either hardware handshake
(RTS/CTS) or software handshake (XON/XOFF).
The same handshake method must be set in both the modem and the communications
software.Ifthisisnotthecase, CRCerrors arelikely tooccurindatatransfers.Ifyouare
using RTS/CTS handshake, the reason may also be the interface cable: If you are using
an RS-232 adapter from 25-pin to 9-pin (also called "mouse adapter"), it is possible that
the RTS and CTS lines (pins 4 and 5) are not connected. Be sure to always use the sup-
plied adapter for this reason.
Another possible error source is the serial interface of your computer. At bit rates of
19,200 bps and higher under DOS, and generally under Windows or OS/2, a UART chip
oftype16550shouldbeused.ThisUARTisequippedwitha16-byteFIFObuffer,allowing
considerably higher transfer rates. Type 8250 and 16450 chips only function reliably at
speeds of up to 9600 bps; individual characters can be lost in the interface at speeds of
19,200 bps upwards, leading to CRC errors.
Why do I always get CRC errors with my modem during Zmodem downloads at
115,200 bps, even though I'm using a UART 16550 with FIFO in my COM port?
The throughput rate for 28,800 bps CONNECTS is just 2000 cps.
ThepoorthroughputistheresultofthelargenumberofCRCerrors.Checkthatyourcom-
puter BIOS settings for the entryIDE HDD BLOCK MODE are set to DISABLED.