Installation guide

22 PV Clinics Installation Manual 21/07/11 01.00 01/12
6. Modbus
6.1 General
Modbus is a simple and robust, polled, industrial communications protocol that has become the de-facto
standard for industrial applications and is now among the most commonly used systems for transferring data
between devices. Transclinic Modules use Modbus RTU serial communications via RS485 because the sig-
nals can be sent over long distances using cost effective, twisted pair cables.
For a complete description of Modbus Protocols, please refer to the
www.modbus.org website.
6.2 Modbus RTU
Transclinics equipment operates using Modbus RTU communications over an RS485 network. This commu-
nication is based on a master-slave structure. A single ‘Master’ device (normally the PLC or PC) manages
the communications within the network. The other devices (Transclinics) act as ‘Slaves’ and only respond to
commands from the Master device.
The communications are carried out in a simple way: The master equipment sends a data information re-
quest or a command to the slave equipment that is selected. The slave equipment receives the request or
command and responds with the confirmation or the requested data.
Fig. 1 Master-Slave Communication in Modbus RTU
Transclinics operate in MODBUS RTU via RS485 because it allows operating at larger distances; it can be
easily installed; and is cost effective. The purpose of this section is not to cover the MODBUS protocol in de-
tail; therefore, we only include this small description.