Toshiba XLTR-200 Manuel d'utilisateur télécharger pdf (Page 25)

points that are found to have their timeout enable selections set to “enabled”

will then have their configured timeout values automatically written to their

assigned “source port” objects. This mechanism provides for a flexible set of

device failsafe conditions to be established on a point-by-point basis.

11.3 Point Configuration

As mentioned in section 1, the Network Gateway Series concept revolves

around a central “point database”, containing the value and access

characteristics for each network. With respect to the Network Gateway Series,

a “point” is simply an object that defines some sort of network access, mapping

and configuration data, as well as a single “value” attribute that can be read

from or written to by various communication ports or protocols.

The only restriction placed on this “central clearinghouse” concept is that only

one port can autonomously update the point’s value, “mirroring” its designated

object for other protocols to access. What this means is that although any

protocol can read from or write to a point’s internal value, most of the time that

point’s value will simply be mirroring a remote data object that resides on one of

the gateway’s subnets. The selection of what a specific point is to mirror is

performed via its “source port” selection.

For example, a point may be configured to contain Toshiba ASD parameter

mapping and Modbus master ID and holding register mapping information.

However, because both of these protocols act as “master” protocols, only one

of them can be allowed to continuously update the point’s value. If both master

protocols could simultaneously update the point’s internal value, it would

erratically alternate back and forth between the values designated by the

Toshiba parameter and Modbus holding register objects. Any “slave” protocol

(Modbus RTU slave, Metasys N2 etc.) can read from or write to a point at any

time, but only the protocol designated by the point’s “source port” assignment

will autonomously update the point’s value independent of any other protocol

traffic.

The “source port” designation also determines where a new point value will be

written to when a “slave” protocol writes a new value to the point. For example,

if a Modbus RTU slave connection is used to write new data that changes the

value of a point, how do we know where this new value will exit the gateway to

arrive at its final destination? The answer is that any new point values written

by “slave” protocols will generate “write” transactions only on the “source port”.

This concept may best be further explained by way of a representative

scenario. For example, let’s assume that the gateway’s RS485A port has been

designated to be a Modbus Master. Let’s further assume that the “Modbus

Master” portion of point #5 indicates an “Address” value of 8 and “Register”

value of 14, and that point #5’s “Source Port” selection is set to “RS485A”.

What this means is that independent of any other gateway traffic, point #5 will

continuously attempt to update its internal value by making requests to the

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Toshiba XLTR-200 Manuel d'utilisateur Page 25