NEC NDA-24233 Communication Procedure, Command/Response Procedure, Abnormal Handshake Procedure

VisuaLink 128/384 Engineering Guide Chapter 1

1.5 Communication Procedure

There is no procedure for communication between a console and VisuaLink as a rule. Therefore, a communication line is presumed to be error-free. When it is remotely operated with a modem, efficient operation may not be expected when a line error occurs. Because of this, in a remote control, a modem with error correction feature shall be used, or VisuaLink shall be checked for operation.

Command/Response Procedure

VisuaLink transmits a confirmation on whether a command is received and the process is completed. After sending a command, please always analyze the transmitted response before issuing a next command. If the next command is issued before a response, an error response such as ''currently processing'' may be returned.

PC Console	VisuaLink
	Command 1
	Response
	Command 2
	Response

(1)Command 1 is issued using the external control port rather than a personal computer.

(2)Analysis of a received command (parameter error, etc.) is implemented.

(3)After an analysis, if it is normal, a normal response is transmitted to a personal computer after transmitting to the remote in communication. However, if it is error response, the error shall be analyzed, and a command shall be either suspended or re-issued.

(4)After verifying that Response 1 is normal, issue Command 2.

Note: After issuing a command from a console, if an alarm emits in VisuaLink, an alarm report may be transmitted before a response to the command.

Abnormal Handshake Procedure

When the VisuaLink receives a report command from a remote unit at a time the VisuaLink is sending a command to the remote unit in communication, the VisuaLink transmits an indication to a PC using the external control port and then transmits a command to the remote unit.

Console VisuaLink Remote

Command 1

Report Command

Response 1

Report

Command 1

NDA-24233 Issue 2 Page 1-5