Figure 2.3 Multi-Access Mode - Advantech EKI-1521 User Manual

2.1.2.2 Multi-Access Mode (Shared COM port mode)
Most of serial devices are connected directly and physically to the PC serial ports via
a cable. The operation system, ex. Windows XP, provides the COM ports that user's
application can access, and control the serial device through the serial cable. This
means that the serial device can be connected to one host and only one application
on this host can handle input, output and control operation on this device.
If you want to run more than one applications to use a serial device, you can employ
EKI serial device servers that provide a virtual COM port for a host or multi-hosts on
an Ethernet network. EKI serial device server is located between hosts and serial
devices. Each serial port on the EKI serial device server can allow max. five host
connections through one Ethernet port or two Ethernet ports. There are two major
operation modes for Multi-Access Mode. First one is broadcast mode; EKI serial
device server handles a command from one application and replies the data from the
serial port to all applications that are connecting this serial port. Another one is polling
mode; EKI serial device server handles the command from one application and reply
to this application only. Query from other applications must be queued and wait for
current process completing.
By using a serial derive server to share serial device, you eliminate the separate
serial lines and serial devices that can be attached to individual hosts. Collecting the
data from these serial devices become more easily and more effectively.
EKI-1521/1522/1524 User Manual

Figure 2.3 Multi-Access Mode

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