Chapter One
Introduction
MAN_105G_1.5
Page
8
The 105U-G is referred to as the 105G for the rest of this document, to clearly differentiate
from normal 105U I/O modules.
Ordering information:
105U-G-MD1
Modbus Master & Slave / DF1 interface
105U-G-PR1
Profibus-DP Slave interface
105U-G-ET1
Ethernet interface - Modbus TCP, Ethernet IP, FTP, HTML, Email
1.1.1
Modbus / DF1 105G
The 105U-G-MD1 can be configured for Modbus master interface, Modbus slave, or DF1.
Modbus is a PLC protocol originally developed by Modicon (now part of the Schneider
group). It became a popular interconnect protocol with many equipment manufacturers.
Modbus is a “master-slave” protocol. One Modbus master controls the Modbus network
communications, which can comprise up to 250 Modbus slave devices. The Modbus master
can read or write I/O values to/from Modbus slaves. The 105G can be configured as either
Modbus Master or Modbus Slave. The variation of Modbus supported by the 105G is
“Modbus RTU”
(also known as “Modbus binary”).
DF1 is an Allen-Bradley protocol (Allen-Bradley is now part of the Rockwell Automation
group). DF1 offers both full-duplex (point to point) and half-duplex (multidrop) operation.
The 105G only supports the full-duplex operation - this is the default DF1 mode on most
equipment. DF1 full-duplex is a “peer-to-peer” protocol. Either DF1 device can initiate
commands to the other device, and both devices will respond to commands from the other
device.
The 105U-G-MD1 has two serial connections - RS232 and RS485, on the bottom end plate
of the module. The serial port provides both RS232 and RS485 hardware connections,
however both connections are paralleled internally - both connections cannot be used at the
same time. Either RS232 or RS485 can be used for Modbus communications,
however only
the RS232 port can be used for DF1
. The serial port must be configured to suit the host
device. Serial data rates between 1200 and 19200 baud may be selected, and character types
with 7 or 8 data bits, even/odd/none parity, and 1 or 2 stop bits may be selected.
The Modbus/DF1 105G has 4300 I/O registers. Each discrete, analogue and pulse I/O point
takes up one register.
1.1.2
Profibus 105G
The Profibus 105G provides Profibus-DP Slave functionality according to EN 50170.
Profibus is a popular automation data bus that originated in Germany and used extensively by
Siemens and other automation suppliers.
The Profibus connection on the 105G is optically isolated RS485 using an on-board DC/DC
converter. The Profibus port has automatic baudrate detection (9600 bit/s - 12 Mbit/s).
The Profibus 105G I/O database has 4300 registers (each of 16 bit value), however the
Profibus interface only supports 416 x 8 bit bytes of I/O, and this limits the amount of I/O
that can be transferred via the Profibus port. Of the 416 bytes of I/O, there is a maximum
244 input bytes and maximum 244 output bytes - that is, if 244 input bytes are used then
only 172 output bytes can be used (416 – 244). Each byte can represent 8 discrete inputs or
outputs, or an 8-bit value, or two bytes can represent a 16-bit value. That is, analogue or
pulse I/O can be transferred as 8-bit registers (1 byte) or 16-bit registers (2 consecutive bytes).
