A control system including control devices with each control device
including a control unit and a display device connected with the control
unit via a dedicated communication line and being capable of display
corresponding to a control state of the control unit. The display device
includes a communication port connected with a control unit and a
communication port connected with a data processing device, and a data
processing section. Further, the data transmission method includes a
dedicated protocol communication transmitting data with a processing
device and a common protocol communication transmitting data with another
processing device. In addition, the control-host computer used in the
control system includes a control unit controlling a control target and a
display device.