IDEC WindSRV - Manual (Page 36)

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assigned IP address. The list of available NICs will include both unique NIC cards and NICs that have multiple IPs
assigned to them. The selection will also display any WAN connections that may be active (such as a dialup connection).
Ethernet Encapsulation
The Ethernet Encapsulation mode has been designed to provide communications with serial devices connected to
terminal servers on the Ethernet network. A terminal server is essentially a virtual serial port: the terminal server
converts TCP/IP messages on the Ethernet network to serial data. Once the message has been converted to a serial
form, users can connect standard devices that support serial communications to the terminal server. Using a terminal
server device allows users to place RS-232 and RS-485 devices throughout the plant operations while still allowing a
single localized PC to access the remotely mounted devices. Furthermore, the Ethernet Encapsulation mode allows an
individual Network IP address to be assigned to each device as needed. By using multiple terminal servers, users can
access hundreds of serial devices from a single PC via the Ethernet network. For more information, refer to
How Do
I.. and Device Properties - Ethernet Encapsulation .
Modem Support
This server supports the use of modems to connect to remote devices, which is established through the use of special
modem tags that become available at the channel-level when a dial-up network connection has been created. These
channel-level modem tags can be used to dial a remote device, monitor the modem status while connected and
terminate the call when completed.
Note: Not all serial drivers support the use of modems. To determine modem support, refer to the specific driver's help
documentation.
When accessing the new modem tags, the channel name can be used as either a base group or topic name. If the
project contains more than one channel definition, users will need to configure the channel names so that each is
unique. This remains true for device names, as well. Channel names can no longer match the device name when the
project needs to be configured to use a modem. The channel name requirements do not apply to projects that are not
using a modem.
In order to be used, modems need to be configured with the operating system through the Control Panel settings. For
specific setup information, refer to the Windows and modem documentation. Once the modem has been properly
installed, it can be enabled by selecting the Use Modem checkbox in the Channel Wizard.
Important: Many new commercial modems are designed to dial-up network server connections and negotiate the
fastest and clearest signal. When communicating to a serial automation device, the modem needs to connect at a
specific Baud (Bits per Second) and Parity. For this reason, we strongly recommend the use of an external modem,
which can be configured to dial using specific Baud Rate and Parity settings. To determine the best modem for a specific
application, check with Technical Support. For examples on how to use a modem in a project, refer to
How Do I... .
Using a Modem in the Server Project
Modems convert the serial data from the RS-232 port into signal levels that can be transmitted over the phone line. To
do this, modems break each byte of the serial data down into bits used to generate the signal to be transmitted. Most
modems can handle converting up to 10 bits of information for every byte of data that they send. To communicate with
a device via modem, it must be able to use 10 bits or less. The following formula can be used to determine how many
bits a specific device is using.
Start Bits + Data Bits + Parity + Stop Bits = Total Bit Count
For example, if using the Modbus RTU driver we can assume that the device is configured to use 8 Data Bits, Even
Parity and 1 Stop Bit (1 Start bit is always implied). When plugged into the formula, it would be 1 + 8 + 1 + 1 = 11
Bits. A normal modem would not be able to transmit data to this Modbus device using these settings. If the Parity is
changed to None, however, the result becomes 1 + 8 + 0 + 1=10 Bits. A normal modem can now be used to transmit
data to this Modbus device.
Some drivers simply cannot use a normal modem connection and cannot be configured to use a 10 bit or less data
format. These devices cannot use standard modems. Luckily, there are manufacturers who provide modems that can
handle transmitting 11 data bits. If the driver falls into this category, users should consult the device's manufacturer for
recommendations on an appropriate modem vendor. Modem operation will be enabled for all serial drivers regardless of
their suitability for modem operation.
Note: For the following example instructions, create a project and set the channel settings to use 10 bits or less for the
connection. Configure the device to use the same settings.