FAQ about Modems , Modem applications and the
SAIA Modem Library.
This information
does not engage Engiby in any cases and are only informative. The document
reports some typical problems occurring with modem application and situations
occurring by Engiby when using modems. Usually the problems are not caused by
an error in the library but by bad modem installation or configuration.
Official information and supports concerning the SAIA Modems and the SAIA Modem
Library are give by SAIA only.
Trick and
Tips
How to trace Modem
activities ?
By putting Modem
application it is very useful or even necessary to have a trace of the modem
activities. Some problems can occur at certain time of the day or in the night.
To help users to trace modem activities, Engiby has developed a useful tool
called NG-Trace. A freeware version of this tool is available on
request. The freeware version include a simple trace buffer for modem
application. For better analysis, an advanced modem buffer version can be
purchased. The NG-Trace is very easy to use and can be connected to the PCD
over any PGU connection : Point-to-point, S-Bus network or S-Bus over modem.
How to realize secure
S-Bus transmission
When a PCD (master)
calls another PCD (slave), how to ensure that all telegrams have been send ? How
to know which telegrams have not been transmitted ? How to repeat the call
if the line has poor quality ? How to take a decision if a telegram cannot
be sent ? All this questions have an answer by using the S-Bus Modem
application with the NG-Configurator.
See more here.
No Manual about the
modem
The well known
modem manufacturer have an Internet site where you can fined a lot of
information about modems. The modems can usually return the manufacturer, modem
type and version. In the HyperTerminal, type the commands:
ATI0
ATI1
And so on.
ATI4 Returns the most important
configuration parameters
ATI7 Returns a detailed modem
identification
The information can show that the modem is identical to a well known modem.
The modem is also able to display, in short form, the supported commands.
In the HyperTerminal, type the commands:
AT$
AT&$
ATD$ Dial command syntax
ATS$ S-registers commands
Modem on all serial
lines with PCD6 and on PCD7.F522
On almost all PCD,
the line 1 has full handshake and can support modem. Other lines can also
support a modem but with restrictions, like outgoing calls only. When
connecting a modem to the PCD6, all lines have full handshake but the Modem
Driver 8 still assume reduced functionality. In this case, use the new Modem
Driver 12. In this Fbox you can manually select the option to 'Full handshake'.
The same situation occurs when an F522 module is plugged on a PCD2. In this
case, the channel 2 can be set to full handshake (HW jumper AND setting in the
Modem Driver 12).
Modem synchronization
How to know in
which baudrate and which mode (LAPM, etc…) modems are synchronized ? Start the
HyperTerminal, use a direct connection to COM x. Send manually the reset and
the initialization strings to the modem. Send manually the dial command. The
modem will send back the connect result once connected to the remote modem.
Note that the displayed baudrate may be different on both modems. E.g. 33600
and 28800. The display is also affected by the X-setting. Usually X4 enable all
response.
How to
send an E-Mail or a Fax by Modem ?
Untill there is no
E-Mail service supported by the PCD use the following tip to send an E-Mail via
modem from a PCD. Some GSM network provider offer services to route SMS messages
to an E-Mail address or a Fax number. Contact your provider to know which
services are available and the corresponding syntax.
For instance, Orange Switzerland : Send a SMS to the number 468 and add mail
ad@srv.ch before your message (ad@srv.ch is the E-Mail address)
New
feature / New version
Modem in PCS1 on port 0
The PCS1 can be
equipped with a Modem PCD2.T813 or T850 on port 0. This port has a special
mechanism which allows the use of the port 0 with the PGU cable and with the
modem for S-Bus PGU with modem. When the modem driver Fbox also want to access
the Modem on this port, it must support a special handshake called 'PGU
Switched'. This option is available from Modem Library version $ 2.3.005. This
version is foreseen for PG5 1.2 but can also be used with PG5 1.1. You also
need at least a Firmware version 090 (or $ 08F) in the PCS.
Typical
problems using modems
No answer from modem
Of course, no
answer from modem can be due to bad cabling, missing power and so on. The
simplest way to test a modem is to start the Hyperterminal program from Windows
and send manually some commands to the modem. If the RX led is blinking as you
type the command, you can assume the power and the cabling are OK.
If the modem doesn't
respond to a reset command (ATZ) it seams to be out of order. An explanation of
the situation is the following: With the reset command, the modem load a
definable profile (E.g. user profile 0). This profile can be defined with the
commands ATYn and AT&Wn (Consult the modem's manual). This profile can turn
off the echo (E0) and set the response mode to silent (Q1). In this case, the
modem will not echo what you type and also not send any OK response. However,
it should display the configuration with the appropriate command (USR: ATI4,
Other : AT&V). Then you can check and correct E0 to E1 and Q1 to Q0. Save
the new profile and tray ATZ again.
NO DIALTON or NO ANSWER
with a large number of ring signal.
If you have set a
large number of ring signals (6 to 10) before the modem should answer the line,
you must adapt the Connect timeout when calling via modem from the PG4/5. N PG4
you can set this time at up to 120 sec. However you may have a NO DIALTON or NO
ANSWERR response already after 50 sec and this is to short for 6 to 10 ring
signals. The modem has also a connect timeout, usually set to 50 sec by
default. To solve the problem you must increase this time by setting the
register 7 to 100 ( S7=100 ). Read also the modem manual.
Cannot dial a correct
number
A problem can occur
if the modem is to fast when dialing. The first digit may be lost for the phone
exchanger. To avoid this problem the modem must wait for the dial tone before
to start dialing. Insert a 'W' character in the Field 'Output prefix' in the
SASI-Modem Fbox.
Modem does not hang up
This is one of the
problem that may lead to unnecessary telephone cost and may avoid the PCD to be
reachable via the modem. General disturbance on the phone line, on the serial
line and via the power line can lead to this situation. This problems can not be
excluded in any modem application. As security, for this kind of situation, the
power hang up output of the SASI-Modem Fbox must be used. Read the detailed
description in the help.
Choice of default bit
settings
Some protocol need
to transmit 8 data characters. Example: S-Bus, DATAD, Modbus RTU. In the other
hand, a lot of modems are not supporting more than 9 bits (8-N-1 or 7-E-1). In
this case, the default bits setting must be set to 8-N-1.
Using different modem
types
Difficulties may
appear when different types of modem are used especially if data compression
and/or error correction are supported at one side only. The modems can have
difficulties to exchange correct data. It may even be totally locked and does
not even hangs up on ATH command and DTR low signal. Incase of doubts, turn off
compression and error correction on both side. In some case it could also be a
good choice to force the baudrate on each side.
Cannot connect to S-BUS
station.
This message is
issued on the PG4 when it cannot communicate with the PCD after the modem
connection is established. A potential problem is the use of error correction.
Problem noticed with USR-33.6 and 3COM-56k PC Card. Adding the command
'&M0' in the PCD configuration solves the problem.
Cannot send SMS
When error
correction is disabled, data transmission is not possible immediately after
CONNECT response is issued by the modem. A delay of 1 to 5 second may be
necessary. Problem noticed with the SMS server of Swisscom.
Using various bits
settings
Using various bit settings
may cause the following problems. The modem adapt it self to the bit settings
on a AT command. If the settings is changed for data transmission the modem can
have problem and send wrong data or even hang up the line.
E.g. The modem is initialized with 7
bits, Even parity, 1 stop.
S-Bus use 8 bits, No parity, 1
stop.
In this case, the default settings should be set to 8-N-1 instead of 7-E-1.
Using various baudrate
Some modem are not
able to change automatically to low baudrate values like 1200 bd. Therefore, a
baudrate suitable to all cases should be used. Special care must be taken when
Pager and SMS services having low baudrate are used. The default baudrate
should be set to a low value.
Unable to send SMS or
Pager message
Case 1
The SMS Center
usually have a limited range of baudrate. If the Modem use an automatic
baudrate it may synchronize to the highest possible baudrate with the remote
modem. The attached computer will not receive the message. In the Call SMS
Fboxes the alternate Init string can be used to force the modem to use a fix
baudrate.
Example for US Robotics and the Swisscom Server, add the command &N3 in the
init string to force the baudrate at 1200.
Case 2
The Call SMS Fbox has a parameter called 'Transmission delay' (default
5.0sec) which delay the message transmission after the modems are connected.
Problem have been noticed if this time is below 6.0 sec. Set a time of 8.0 to
10.0 sec and tray again.
Case 3
For swiss customer only. You may have difficulties to send SMS messages,
when your have a communication provider other than Swisscom. In this case you
must force the modem to use Swisscom services by adding the prefix 10741 before
the SMSC call number in the Call SMS Fbox. This prefix is not valid when you
are using the GSM-Text protocol on a GSM modem.
Case 4, for GSM modem with 'GSM-Text' protocol
The preliminary condition is to be connected to the network. This should be
displayed by LED on the GSM modem. See the manual. Then you must have set the
PIN code. You can also lock it so it is always valid after power down. If these
conditions are OK you must be able to make a phone call (ATD…phone number).
Tray it out. If you have a prepay card, you need a minimum value on the card
depending on the provider. You must set the correct service center number
according to your SIM card. You cannot send a message to another provider.
Hang up not detected
As to switch the
modem to command mode, a silent of 1.5 sec must be respected before to send the
+++ string. If the PCD is in S-Bus (slave or master), the firmware may continue
to send S-Bus telegrams to the partner station during the silent delay. The
modem will not recognize the +++ string as the escape to command mode. In this
case the modem must be correctly configure to hang up if DTR is low. This
problem was discovered using the modem on port 0, without DTR signal. Fixed in
version $ 2.1.252. This problem can also be solved by using the power hang up
function.
Modem don't want to dial
on PCD port 0 or 2
As to connect a modem
on port 0 or 2 of PCD 1 and 2 the library $ 2.1.252 is required. The DTR signal
on the modem must be set to High level to enable the modem to dial and
communicate. You should connect the RTS signal also to DTR terminal on the
modem. You may also need to initialized your modem to ignore DTR (Example:
&D0 for USR Sportster).
Unable to communicate
via port 0
As to connect a
modem on port 0 of PCD 1, 2 and 4, the library $ 2.1.252 is required. The DTR
and the DCD signals must not be connected to the PCD. This may force the port 0
in PGU mode and will not allows the PCD to work in standby = S-Bus Slave or
C-Mode. On port 0, PGU cables force the port in PGU mode and disable Modem
support. After PGU have been connected, the PCD must be switched off and on again
(this is not anymore required from library version $ 2.3.005).
No command accepted by a
GSM modem
At power up and
after a reset, a GSM modem can takes long time (up to 1 minute noticed with
INSYS modem) before to accept command on the serial line and to be connected to
the GSM network.
The Siemens M20 GSM Modem does not support autobauding. You must manually
initiate the modem to a fix baudrate, E.g. 9600, 8-N-1. Don't forget to save
this settings in the modem profile. Set also the default baudrate in the Modem
Driver to 9600, 8-N-1. If you use a Page or a SMS service, you may have problem
because each Service Center has its own settings (remark not valid for the
GSM-Text protocol). You can try to force the baudrate and the bits settings in
the Call Pager/SMS Fbox. Test it. Good luck ! It may work.
Tip : To SMS wia a GSM modem, you should use directly the GSM services
integrated in the GSM modem. This can be done by using the 'GSM-Text' protocol.
No data communication
with GSM modem Siemens M20
To be able to
exchange S-Bus telegrams with an analogue Modem, it is necessary to set the GSM
modem in the correct Data mode. The GSM modem should be initialized manually
with the command:
AT+CBST=7,0,1 or
AT+CBST=7,0,0 depending on the provider.
Call your provider or Siemens for more details.
Supported Voice and DTMF
features
The modem itself is
able to give you the allowed parameter for the voice mode commands by typing
the following syntax:
AT+FCLASS=?
or AT#CLS=?
If the value 8 is in the response, the mode should support voice mode. Although
it is not ensured that it support all the DTMF feature we need. Despite this
standard syntax a modem can ignore this syntax for some advanced features and
responds with ERROR or just OK without values (noticed with A-Link modem on
DTMF commands).
ISDN modems usually don't support DTMF.
GSM modems usually don't support DTMF but you can send the same commands by SMS
and use the Poll SMS Fbox. See the appropriate description.
Incoming calls not
detected or even no modem detected
Modem presence as
well as incoming calls are detected by the states of the control lines. If the
modem is not detected the Modem Driver (Modem state = No Modem) when being
connected and powered up, it can be a cabling problem with the control lines.
If the modem is detected but incoming calls are not detected, it should be a
missing DCD connection. Such a case has been found when using a serial line
analyzer with a special cable. If the cable is foreseen for 'simple' analyze,
it may omit the DCD control line.
The modem is
continuously reset and initialized
This may appear
with an S-Bus PGU Modem configuration. It is noticed by the fact the FW byte is
running up to about 30 and restart from 0. But it never reach the end value 50.
Reset and Init string are continuously sent to the modem. This can be due to
bad connection (control lines, ground) or a defective modem. Possibly, the
modem starts with a bad configuration regarding handling of control lines. See
the document 'Modem application' for more details. But there is also a know FW
bug producing this behavior when T813 or T850 modems are reset using directly
the reset signal on the IO-Bus (base address+3). To reset the modem, you should
rather use the reset inputs of the new Modem Driver 12.
The Message or the ID is
not transmitted properly with Call Master Message/ID
This has been
noticed with the Citect supervisor which expect a first message from the PCD
before to start the S-Bus driver. Disturbance characters may be added before
and/or after the message and avoid the Citect to understand the message. This
can append when error correction is not activated between the 2 modems. Error
correction is disabled by default in the MODMBASE.DAT file because S-Bus
doesn't need it. To solve the problem of the disturbed message, enable the
error correction (E.g. for T813 remove the \N0 command).
Only one PGU call
successful
This situation
occurs for instance when the option Reset = Emergency is selected. It should be
due to the fact that the default baudrate set in the Modem Driver Fbox is not
the same as the one in the S-Bus Modem configuration. At the end of an incoming
call the functioning of the Modem is checked. If this check is executed with a
different baudrate, the modem will be put in the wrong baudrate for the next
PGU call.
This dangerous situation also exist when only the life check option is
activated.
It is strongly recommended to use the same baudrate in the Modem Driver than in
the S-Bus Modem configuration.
Unable to take the line
for outgoing calls
This problem has
been noticed with PCD2.T813 modem on Siemens PBX of type Hicom 150 and Hipath
3000. A phone to the same line is able make any calls. Incoming calls are
correctly answered but outgoing calls (for instance SMS and Pager) by the Modem
Driver, ends with No Dial tone or a Timeout error. The problem may be due to a
bad setting in the Siemens PBX : The line should NOT be configured as
'Hotline'. If this don't solve the problem, tray to use another (external)
Modem.
DTMF Command not
acknowledged
After an incoming by a phone device is answered, it is not possible to give
DTMF commands. The commands are not acknowledged with positive tone nor with
negative.
Possible problems :
Case 1
The new Modem PCD2.T813Z42 is not anymore compatible with the former
PCD2.T813 concerning the DTMF commands. You need a Modem library version $
2.3.005 at least and you must select the new Modem type PCD2.T813Z42 (replace
existing Modem Driver Fbox in the Fupla file).
Case 2
If the CPU cycle time is long (above 200 ms), the time to handle a DTMF
command can be longer than the Inactivity timeout. Especially DTMF commands
take several CPU cycle to be handled. You may fix the problem by setting an
higher timeout (e.g. 30.0 sec) but you may encounter further problems unless
you have a cycle time less than about 100 ms.
Known problems with the Modem Library
Call repetition with SMS
and Pager
Error up to version SP 2.2.120. Fixed in $ 2.2.121.
Sending SMS and Pager messages, when the call is not answered by the server
(timeout, bus,...), the recall mechanism of the Call SMS Fbox is not always
activated. Therefore, it is important to set also a recall count in the Modem
Driver Fbox.
Call started during
incoming call
Error in versions 2.3 up to Beta 2.3.050. Fixed in $ 2.3.051.
When a call is started during an incoming call, the call is started but after
modem connection, the port is not correctly assigned.
Send SMS or Pager not
correctly repeated
Error fixed in
version $2.3.054.
In case of SMS/Pager Call error, the repetitions did not repeat with the same
message but used the next active message (if any).
Quality problems
Diagnostic error with
SAIA Modem
Problems found with
SAIA modems PCD2.T850. This modems have problems to adapt itself to the PCD bit
settings. If you want to exchange data with S-Bus, you may set the default
setting to 8-N-1. But the modem still respond with 7-E-1 (or vice versa) and this
case a framing or parity error. However, it should be possible to ignore this
error and the data exchange in S-Bus should works. The modem change its
settings once it receive data from the opposite site in 8-N-1.
ISDN Modem on S0-Bus
(Don't mix up the
ISDN S0-Bus with SAIA S-Bus 0 which is sometimes used to identify
the Break mode). If you connect a PCD2.T850 module in parallel with an ISDN
phone on the same bus, the phone may not works anymore. This is an hardware
problem of the first series of the PCD2.T850 modules.
S-Bus communication not
possible
This has been
detected with a USR-Sportster 56K Voice Fax-modem. The modems was synchronizing
at 14400 bauds and the serial line was also switched to 14400 instead of 9600.
The command &B1 (Fix line baudrate) did not help. But the command &N6
(Connection baudrate fixed to 9600) solved the problem.
Modem don't want to dial
Noticed with T813
and USR-Robotics 56K but can occur with other type too. The modem refuses to
re-dial the same number after some unsuccessful calls. The modem store the
number in a black list'. When the same number is used in a ATD command, an
error is returned. This feature is usually not described in the modem manual.
Solution: switch off the modem and on again. Use the power hang up output. In
modem libraries version 2.2.100, the Modem Driver display the error
'Blacklisted' in this case.
Bad supply
Noticed with
USR-Robotics 33.6K. This is a rare problem. Using the bad power supply, the
modem was working fine until it has to switch DCD signal to High. Other control
signals was drooped low and cause the modem to hang up immediately.
Modem cannot establish a
connection
Problem noticed
with USR-Sportster 56K and USR-Sportster 33.6K. Using low baudrate (1200 bds)
the modem are not able to communicate. The Modems hang up before to set the DCD
signals.
Modem don't hang up
Noticed with
Micronet Shuttle 3000. At the end of a SMS call, the Modem don't want to hang
up the line. The problem seems to appear only when Error correction is
disabled. Solution: switch off the modem and on again. Use the power hang up
output.
DTMF don't works
Problem found with
ZyXel U-1496. The modem supports Voice features however DTMF seems not to be
detected. Is a FW update possible ? I don't know. Furthermore, almost all ISDN
and GSM modems does not support DTMF incoming signals and cannot be used with
the DTMF library.
Supervisor problem
The Citect driver
for modem has the following problem (state June 2000). The modem is handled by
Windows to establish a modem call. After the connection, the 'normal' S-Bus
driver is started. This cause the DTR and the RTS signals to be toggled like
for the S-Bus on RS 485. The Modem will immediately hang up the line or ignore
telegrams. The modem must be configured to ignore DTR Low AND RTS Low
signals.
Problem when the PCD call
the Citect : The supervisor hang up after some seconds. It seams that the
Citect, for optimization reason decide to hang up the line even if no user
action decide to. Problem to be solved by Citect.
Open points
These are questions
remaining without clear response or solutions for now. Maybe somebody have a
good idea ?
Watchdog
How to realize a
safe modem watchdog ?
An idea is to count the
number of ring coming from the modem. If more than x rings (for instance 10)
are counted by the Incoming call Fbox, we can assume, the modem is not working
properly and switch Off and On the power supply. But if the modem is
deadlocked, it will probably not send the ring message to the PCD. For a safe
solution, the ring should be counted by an external device (more safe than the
modem). The external device should be able to reset the modem in case of
problem.
Does such a device exist on the market ?
|
|
Back to Engiby main page Engiby / 13.10.2005 |
