MDS TransNET 900 Specifications download pdf (Page 65)

MDS 05-2708A01, Rev. E MDS TransNET Ref. Manual 55

All Remotes synchronize to a corresponding Master. This can be the “real

Master” (the

MODE M unit), or it can be a repeater “Extension” that derives

synchronization from the “real Master.”

Payload polls/packets broadcast from the network Master will be repeated to

all levels of the network, either directly to Remotes, or through network

repeaters—the Extension station. The targeted Remote responds to the poll

following the same path back to the Master.

Synchronization Messages

Remotes acquire synchronization and configuration information via

SYNC

messages. They can synchronize to the Master (the

MODE M unit) or to any

valid Extension (a

MODE X unit).

The Master will always transmit

SYNC messages. An Extension will only

start sending

SYNC messages after synchronization is achieved with its

Master.

The ability to synchronize to a given radio is further qualified by the sender’s

Extended Address (

XADDR) and by the receiver’s Synchronization Qualifiers

(

XMAP, XPRI, and XRSSI).

When a primary is specified (

XPRI is 0...31), a radio will always attempt to

find the primary first. If 30 seconds elapses and the primary is not found, then

the radio attempts to synchronize with any non-primary radio in the

XMAP

list.

Once every 30 minutes, if a primary is defined, the radio will check its

synchronization source. If the radio is synchronized to a unit other than the

primary, then the current

RSSI value is compared to the XRSSI value. If RSSI

is less than

XRSSI (or if XRSSI is NONE) the radio will force a

loss-of-synchronization, and hunt for the primary again (as described in the

previous paragraph).

By default, Extensions (and the Master) begin with

XADDR 0. Synchroniza-

tion qualifiers are set to

XMAP 0, XPRI 0, and XRSSI NONE, respectively. This

default configuration allows any radio to hear the Master. When an Extension

is added, the extended address of the Extension radio must be set to a unique

value. All Remotes that need to hear that extension can specify this either by

designating the extension as the primary (

XPRI), or by including it in their list

of valid synchronization sources (

XMAP).

9.3 Using AT Commands

A TransNET network may be configured to support protocols employing

Hayes-Compatible modem commands through the radio’s AT Mode. In this

mode, TransNET units can provide a communications replacement for

dial-up modems where the RTUs and the protocol do not contain address-

ability, and the establishment of a direct-communications link is the only way

to determine if the RTU has data ready to be sent. This requirement is

common in many older SCADA systems which were developed for direct

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MDS TransNET 900 Specifications Page 65

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