aerl
COMMS MANUAL
COOLMAX SR
Australian Energy Research Laboratories, Pty.Ltd
AER07.004 – Version G2 v9
13
th
January 2016
7 of 21
3.4
SHIELDING
Correct shielding practice is important for error free communications. Incorrect shielding can cause
more interference than unshielded cables would experience. Shields should be linked between
each wire segment along the network but only grounded in one place. The following paragraphs
explain how to achieve this.
The shield should be wired through the entire network independently of the ground and connected
to ground at the end of the network and nowhere else in the network. This is shown at the right
hand end of the example network in
Figure 2.
3.5
MODBUS TERMINATION
A 120 Ω resistor needs to be wired between the Modbus-A and Modbus-B lines at either end of the
linear network in order to terminate both ends of the network. At the far end of the network the
resistor can be simply installed into the last terminal block.
If no Modbus-Ethernet Bridge adapter is present on the network the same terminal block style
termination can be made on the other end of the network. However, if a Modbus-Ethernet Bridge
adapter is present on the network, it can be used to terminate the network by wiring a termination
resistor across Modbus-A and Modbus-B on the unused header.
3.6
MODBUS MEMORY MAP (DISCRETE INPUTS)
Single−Bit (Read−Only)
Returns :
0 to 255 (
byte
data type) 0x00 to 0xFF (i.e. 8 Bits)
Notes :
When a request is sent to read a discrete input, a byte is returned containing the values of 8
consecutive inputs, with the addressed input as the LSB. If the returned input quantity is not a multiple
of 8 bits, then the final data byte is padded with zeros.
Memory
Offset
Input Address
Description
Input
Range
Data
Range
Read/Write
Comment
−
10000
−
−
−
−
−
0
10001
ACTIVE EVENTS
System Power
Bit
0 or 1
Read−Write
0
Event
Cleared
1
Event
Triggered
1
10002
ACTIVE EVENTS
Low Out Voltage
Warning
Bit
0 or 1
Read−Write
0
Event
Cleared
1
Event
Triggered
2
10003
ACTIVE EVENTS
Low Out Voltage Fault
Bit
0 or 1
Read−Write
0
Event
Cleared
1
Event
Triggered
3
10004
ACTIVE EVENTS
Low Out Voltage
Gen−Set
Bit
0 or 1
Read−Write
0
Event
Cleared
1
Event
Triggered
4
10005
ACTIVE EVENTS
High Out Voltage Fault
Bit
0 or 1
Read−Write
0
Event
Cleared
1
Event
Triggered
Important
