Introduction
Communication Modes
The ESP901 and ESP902 Serial Servers enable communication with serial devices over a LAN or WAN. Serial devices no longer are limited to a physical connection to the PC COM port. They can be installed anywhere on the LAN using TCP/IP or UDP/IP communications. This allows traditional Windows PC software access to serial devices anywhere on the LAN/WAN network.
Direct IP Mode
Direct IP connections allow applications using TCP/IP or UDP/IP socket programs to communicate with the asynchronous serial ports on the Serial Server. In this type of application the Serial Server is configured as a TCP or UDP server. The socket program running on the PC establishes a communication connection with the Serial Server. The data is sent directly to and from the serial port on the server. When using UDP protocol the server can be configured to broadcast data to and receive data from multiple IP addresses.
Virtual COM Mode
Install Virtual COM Mode allows the user to add a driver, to provide a virtual COM port on the computer. The new COM port shows up in the Device Manager. Windows programs using standard Windows API calls are able to interface to virtual COM ports. When a program on the PC opens the new COM port, it communicates with the remote serial device connected to one of the ports on the Serial Server.
After connection, the LAN is transparent to the program and serial device. Applications are able to work just as if the serial device is connected directly to a physical COM port on the computer. The virtual COM port software converts the application’s data into IP packets, sends it across the network to the Serial Server, which converts the IP packet back to serial data and sends the data out a serial port located on the Serial Server.
To use this mode, the Serial Server must be set to either TCP/server or UDP/server with a designated communication port number. The virtual COM driver is the TCP or UDP client.
Introduction
Paired Mode
Paired Mode is also called serial tunneling. In this mode any two serial devices that can communicate with a serial link will be able to communicate using two Serial Servers and the LAN.
Two Serial Servers are connected to a network, one configured as a TCP or UDP client and the other as a TCP/UDP server. When setting up the server the remote IP address section must contain the address of the client. This will allow the client’s IP address to pass the IP address- filtering feature of the server. Conversely, the Remote IP address of the client must contain the server’s IP address. Both communication port numbers must be the same.
Heart Beat
The Heart Beat protocol connection provides a reliable communications connection in Virtual COM Port Mode or with Paired Connection Mode. This feature restores the connection if communications are temporarily lost at either end due to loss of power or Ethernet connection.
Without this feature a device that loses a connection and stops communicating would not be able to reconnect without human intervention. A TCP data connection can be lost when there is a power failure or temporary loss of an Ethernet connection on either the client or server. If a loss occurs the Heart Beat feature will try to reconnect the TCP data connection every five seconds until communications is established again. The Heart Beat feature is available for use in Virtual COM Port Mode and Paired Connection Mode. This is not available when using a UDP application.
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