User manual

Chapter One Introduction
MAN_905G_1.16 Page 14
1.2.1 On-board I/O
The 905G has eight on-board discrete I/O. Each I/O point can be used as either a discrete
input (voltage free contact input) or discrete output (transistor output) - an I/O point cannot
be used as both input and output. Each I/O point is linked to two separate I/O registers in the
database - one for the “input” function and one for the “output” function.. If the output
register is set “on” by the fieldbus or by a radio message from a remote module, then the
905G will automatically set the input register for the same I/O point to “off”. This means that
the output register has priority over the input register - if there is a conflict, the input value
is ignored.
The 905G also has three internal inputs linked to I/O registers:
♦ Supply voltage status - if the normal supply fails, this status is set on.
♦ Low battery voltage. The 905G has an internal battery charger to trickle charge a back-
up battery. If the battery voltage is low, this status is set.
♦ Battery voltage - the actual value of the connected battery voltage.
1.2.2 I/O Expansion - 105S modules
The 905G provides eight on-board discrete I/O. Where additional I/O is required, 105S
modules can be connected to the RS485 port of the 905G modules.
Note: 105S modules cannot be connected to the 905U-G-MD1 unit (as this unit uses the
RS485 port for Modbus or DF1 communications), unless this unit is configured as
“Repeater-only” and does not have a host device connected.
1.3 The Wireless Network
The 905G can communicate with up to 490 other addresses - this could be 490 other 905U
modules, or in the case of 905K modules, it could be many thousands of modules (as many
905K modules can share the same address). 905G modules may take up more than one
address under some circumstances.
Any 905G or 905U module can act as a radio repeater for other modules - that is, radio
messages can be passed onto other modules. Up to five repeater addresses can be configured
for messages transmitted to a 905G module.
Each module can have a unit address between 1 – 95, but the 905G also recognizes repeater
addresses in conjunction with the unit address as the module “identifier”. Hence module #2
is recognized as different to #2 via #57 - #57 being a repeater.
1.3.1 905U to 905G Network
In the wireless I/O system, the 905G acts as a normal 905U module (this covers 905U I/O,
105S I/O, 905U-K and 905U-C modules).
905U modules transmit messages to the 905G address and the 905G acknowledges these
messages like a normal 905U module. When a 905G transmits messages to change remote
outputs, it will "re-try" if it does not receive an acknowledgment, like a normal 905U module.
Remote 905U modules can connect to 105S modules in the normal way. The 905G host can
access I/O on 105S modules by using the intermediate 905U as a repeater.