Note: Synchronous Applications typically are mainframe computer based. Standard dial-up ISP is NOT synchronous.
This section contains information about:
This section will apply when you want the modem to work with devices that communicate using synchronous protocols (i.e., mainframe computers). The Courier 56K Business Modem must be connected to a synchronous serial port.
There are two ways to operate your modem in analogue synchronous mode:
| Dial Using | Means |
| V.25bis Software | Configuring the modem to enter synchronous mode when you power it on. Then, running communications software that uses the V.25 bis protocol to control the dialing process. |
| AT Commands | Configuring the modem to dial out using AT commands and then switching to synchronous mode once a connection is made. |
The information below describes device requirements.
Note: Find out what hardware and software you need before proceeding.
You will probably have to purchase and install a synchronous adapter card. These cards provide:
Obtain a shielded serial cable with a male DB-25 connector on one end and a connector on the other end that is appropriate for your synchronous serial port. Your modem provides an EIA-232 interface through its serial port.
Transmit and Receive synchronous timing pins are required at the EIA-232 interface, so pins 15 and 17 are required. The modem transmits timing signals through pin 15 and receives timing signals through pin 17.
Note: The serial cable included with your modem only supports asynchronous mode.
The devices at both ends of the link must use the same synchronous protocol.
Ask your network administrator about the software support (for example, a specific communications package) that you need to log into the network.
During synchronous operations, transmit and receive clocks at both ends of the phone link control the precise timing of the data flow. The communications equipment at the remote device, your modem, and your computer must all handle the data at the same speed.
Your modem is usually the source of the transmit clock timing signals and sends them to your computer over the EIA-232 interface. Your computer’s rate will follow the connection rates.
You can use the Courier 56K Business Modem in either smart or dumb mode (determined by the position of DIP switch 8).
If you are using your modem on a leased or dedicated line, it is set to &L1, and the remote modem has a comparable setting, the modems automatically connect when they are powered on. They also reconnect, without any operator intervention, if a disturbance on the line is severe enough to break the connection.
For example, use a terminal/software setting of 9600 bps and, if both modems have the capability, they will connect at 9600 bps.
| &B1 | Fixes the Courier 56K Business Modem's serial port rate at the same rate you selected when setting up your communications software. |
| &S2 | Causes the Courier 56K Business Modem to send a Clear to Send (CTS) signal only after it sends the Carrier Detect (CD) signal, that is, only after it connects with the remote modem. |
| &H1 | Enables hardware (CTS) flow control. |
| &L1 | Forces the modems off hook at power on and enables them to re-establish the connection should it be broken (for leased lines only). |
| &W | Writes the settings to nonvolatile memory (NVRAM) as power-on defaults. |
Note: We recommend using the &S2 setting to delay CTS until after the connection is made, as a precaution.
If the modems are in the process of connecting or reconnecting, the Courier 56K Business Modem interprets any keyboard data entry, including an accidental key stroke, as a key-press abort, and hangs up. Delaying CTS until after carrier detection prevents this from happening. However, you have to set the Courier 56K Business Modem for hardware flow control by sending AT&H1.
If your software or machine does not support Clear to Send (CTS), don't include &S2 and &H1 in the command string as suggested above. But keep in mind that if the modems fail to connect or reconnect, the reason could be a keypress abort.
Note: If the modems cannot restore the connection and you did not set the Courier 56K Business Modem to &S2, the reason could be a keypress abort. If the problem persists, however, you may need to call your telephone company to have them check your line.
To make synchronous connections using V.25 bis communications software, you must first configure your modem using AT commands. Once the modem is configured, run your communications software.
Before you Attempt to connect to a synchronous network, you must first configure your modem using an asynchronous device, such as a terminal or a computer running standard asynchronous communications software.
| For your modem to | Command |
|
Dial using the BISYNC protocol. Your modem and the remote device must use the same 8-bit data format. The character length must be 7 bits and either ODD or EVEN parity (ODD is preferred), or 8 bits and NO parity. |
AT&M6 |
| Dial using the High Level Data Link Control (HDLC) protocol. | AT&M7 |
Example: Sending AT&M7&W would select HDLC.
| For an offline clock speed of | Command |
| 1200 bps | AT%N2 |
| 2400 bps | AT%N3 |
| 4800 bps | AT%N4 |
| 7200 bps | AT%N5 |
| 9600 bps | AT%N6 (Default) |
| 12000bps | AT%N7 |
| 14400 bps | AT%N8 |
| 16800 bps | AT%N9 |
| 19200 bps | AT%N10 |
Example: Sending AT%N10&W selects an offline clock speed of 19200 bps.
If &Nn is set for 2-16, the Courier 56K Business Modem ignores the &Nn rate and uses the &Nn rate as the online connection rate.
To set the connection rate to Command Variable AT&N0 (Default) Reserved AT&N1 1200 bps AT&N2 2400 bps AT&N3 4800 bps AT&N4 7200 bps AT&N5 9600 bps AT&N6 12.0 Kbps AT&N7 14.4 Kbps AT&N8 16.8 Kbps AT&N9 19.2 Kbps AT&N10 21.6 Kbps AT&N11 24.0 Kbps AT&N12 26.4 Kbps AT&N13 28.8 Kbps AT&N14 31.2 Kbps AT&N15 33.6 Kbps AT&N16 Example: Sending AT&N10%N10&W selects a connection rate and an offline clock speed of 19200 bps.
We recommend that you fix the rate between the computer or terminal and Courier 56K Business Modem (%Nn) and that you set the connection rate (&Nn) to match. This avoids dramatic changes in the rate produced when the connection rate adjusts to the offline clock speed.
Depending on the setting of the Xn command, the modem displays normal or extended synchronous result codes. Extended result codes provide more detailed information. Don’t be concerned if synchronous result codes do not appear on your screen; they are intended for your communications software.
By default, your modem is set to X1 for extended result codes. To change to normal result codes, send ATX0 to the modem.
Example: Sending ATX1&W selects extended result codes.
| For your modem to | Command |
| Disable Auto Answer. | ATS0=0 (Default) |
| Enable Auto Answer. | ATS0=1 |
Note: Due to the nature of synchronous dial-up, if AA isn’t set up in either the hardware or the software, the Courier 56K Business Modem auto answers only on the fourth ring.
Alternatively, you can combine all the previous commands into a compound command, like this: AT&M7&N10%N10X1S0=1&W
This tells the modem to use the HDLC protocol for dialing, an offline clock speed and connection rate of 19200 bps, display extended result codes, auto answer incoming calls, and write these settings to NVRAM.
Your communications software, which must support V.25 bis, handles the dialing. Once the synchronous connection is made and the modem is in synchronous mode, V.25 bis commands are no longer necessary and are ignored. For dialing instructions, refer to the manual included with your communications software.
Since your modem cannot accept commands once it is connected in synchronous mode, you cannot use the ATH (hang-up) command or +++ (the escape code).
The only way for the modem to disconnect is to drop its Data Terminal Ready (DTR) signal. Either power off the Courier 56K Business Modem or use your communications software (check the software user’s manual for instructions).
Once you've completed a synchronous session, you can switch back to asynchronous mode by flipping DIP switch 10 ON and then turning the power of the Courier 56K Business Modem back on. The Courier 56K Business Modem cannot switch between synchronous and asynchronous modes while a call is connected.
To use AT commands to dial, you must set the modem to enter online synchronous mode after you dial. Then, you dial the remote device’s number using AT commands. Once the remote device answers, the modem switches to synchronous mode and starts sending synchronous timing signals to your computer.
Because the modem will not accept commands when it is in synchronous mode, you must configure it in asynchronous mode before connecting to a synchronous network.
The Courier 56K Business Modem always generates the Transmit clock-timing signals when in synchronous mode.
Note: Data Terminal Ready (DTR) override must be OFF when using modem in online synchronous mode. Use &D1 or &D2. See the Controlling EIA-232 Signaling section in this guide.
The device you are calling should also be set to the equivalent of B0 , which tells the modem to use the V.25 answer sequence, and &X0, which identifies the modem as the source of synchronous timing signals.
First try a variable connection rate of &N0. If that doesn't work, try a fixed connection rate of &N6 (9600 bps) or &N3 (2400 bps).
| For your modem to | Command |
| Disable automatic answering | ATS0=0(Default) |
| Enable automatic answering | ATS0=1 |
Note: Due to the nature of synchronous dialup, the Courier 56K Business Modem auto answers only on the third or fourth ring.
Example: AT&M1DT5551234
Alternatively, you can combine all the previous commands into a compound command, like this: AT&F0B0&X0&N0S0=1&M1DT5551234
This tells your modem to load the "no flow control" factory template and then use the ITU answer sequence, making your modem the source of timing signals. This command sets a variable connection rate and causes your modem to auto-answer incoming calls, switch to online synchronous mode after connection, and then dial 555 1234.
There are two methods of autodialing a stored telephone number. You can have the modem dial the stored number either when it receives the Data Terminal Ready (DTR) signal from your computer or at power-on/reset.
For example, AT&Z0=T18475551111, stores the telephone number 847 555 1111, and tone dial.
| For the modem to dial when | Type |
| It receives the DTR signal from your computer | ATS13.3=1&W |
| Modem is reset | ATS13.4=1&W |
When one of the following events occurs, the modem returns to asynchronous Command mode:
Because the Courier 56K Business Modem will not accept commands when it is in synchronous mode, you must configure it in asynchronous mode before trying to connect to a synchronous network.
Then you can set the Courier 56K Business Modem to dial the remote device at power-on, when it receives the DTR signal from your computer, or when you press the Voice/Data switch.
Once the remote device answers, the Courier 56K Business Modem switches to synchronous mode and starts sending synchronous timing signals to your computer.
The device that you are calling should also be set to the equivalent of B0, which tells it to use the ITU answer sequence.
| For your modem to | Command |
| The Courier 56K Business Modem sends transmit clock timing signals to the DTE over the serial interface. DTE rate follows the connection rate. | AT&X0 (Default) |
| The DTE sends transmit clock timing signals to the Courier 56K Business Modem over the serial interface. Typical use: multiplexed leased lines. | AT&X1 |
| The Courier 56K Business Modem sends receiver clock timing signals, which are looped to the transmit clock and sent to the DTE over the serial interface. Typical use: systems that require synchronisation of data flowing in both directions. | AT&X2 |
Try a variable connection rate first, AT&N0. If that doesn't work,
try a fixed connection rate of &N10 (19.2 Kbps), &N6 (9600 bps),
or &N3 (2400 bps).
| Command | Rate | Command | Rate | |
| AT&N0 | Variable (default) | AT&N20 | 32000 bps | |
| AT&N1 | Reserved | AT&N21 | 33333 bps | |
| AT&N2 | 1200 bps | AT&N22 | 34666 bps | |
| AT&N3 | 2400 bps | AT&N23 | 36000 bps | |
| AT&N4 | 4800 bps | AT&N24 | 37333 bps | |
| AT&N5 | 7200 bps | AT&N25 | 38666 bps | |
| AT&N6 | 9600 bps | AT&N26 | 40000 bps | |
| AT&N7 | 12 Kbps | AT&N27 | 41333 bps | |
| AT&N8 | 14.4 Kbps | AT&N28 | 42666 bps | |
| AT&N9 | 16.8 Kbps | AT&N29 | 44000 bps | |
| AT&N10 | 19.2 Kbps | AT&N30 | 45333 bps | |
| AT&N11 | 21.6 Kbps | AT&N31 | 46666 bps | |
| AT&N12 | 24 Kbps | AT&N32 | 48000 bps | |
| AT&N13 | 26.4 Kbps | AT&N33 | 49333 bps | |
| AT&N14 | 28.8 Kbps | AT&N34 | 50666 bps | |
| AT&N15 | 31.2 Kbps | AT&N35 | 52000 bps | |
| AT&N16 | 33.6 Kbps | AT&N36 | 53333 bps | |
| AT&N17 | 28000 bps | AT&N37 | 54666 bps | |
| AT&N18 | 29333 bps | AT&N38 | 56000 bps | |
| AT&N19 | 30666 bps |
If the Courier 56K Business Modem is set to a fixed rate, and the remote device is not set to the same rate, the modem hangs up.
Courier 56K Business Modems cannot connect at 21.6 Kbps or higher in synchronous mode.
HST and V.FC modulations do not support synchronous communications.
For example, to store 847 555 1111, and tone dial, type AT&Z0=T18475551111
Use the following table to determine which command you need to send to your modem for the dialing method you choose.
| For your Courier 56K Business Modem to dial | Command |
| When it receives the DTR signal from your computer. | ATS13.3=1&W |
| When you power your modem on or reset it. | ATS13.4=1&W |
| When you press the Voice/Data switch. | ATS32=4&W |