aerl
COMMS MANUAL
COOLMAX SR
Australian Energy Research Laboratories, Pty.Ltd
AER07.004 – Version G2 v9
13
th
January 2016
19 of 21
If no CAN-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 CAN-Ethernet Bridge
adapter is present on the network, it can be used to terminate the network by wiring a termination
resistor across CAN-H and CAN-L on the unused header.
OVERVIEW
3.7.1
Hardware
The CAN hardware interface used is compatible with the CAN 2.0B standard. The supported bit
rates (bits per second) are 1 Mbps, 500 kbps (default), 250 kbps, 125 kbps, 100 kbps and 50 kbps.
3.7.2
Software
The CAN protocol uses data frames for most communication. Remote frames are also enabled. All
measurement data is transmitted using IEEE single-precision 32-bit format (IEEE 754) with most
significant byte (MSB) sent first.
Bit Length
1
11
6
8 Bytes
16
2
7
Start
Identifier
Control
Data Field
CRC
Ack
End
Figure 2 - CAN Data Frame
3.7.3
Identifier
The identifier field has been split into two sections for the COOLMAX SR. Bits 10-5 contain the
device identifier and bits 4-0 contains the message identifier associated with that device, as shown
below.
10
5 4
0
DEVICE IDENTIFIER
MESSAGE IDENTIFIER
Figure 3 - CAN Device Identifier Address Format
3.7.4
Data Field
The data field in all frames is fixed at 8 bytes (64 bits) which allows space for two IEEE 754 32-bit
floating point variables as shown in the Figure below. The data field is sent and expected to be
received least significant byte first. This allows a direct overlay of a float[2] array and char[8] array
on a little endian processor.
High float
Low float
s eeeeeeee mmmmmmmmmmmmmmmmmmmmmm
^ ^
^ ^
^
63 62
55 54
32
s eeeeeeee mmmmmmmmmmmmmmmmmmmmmm
^ ^
^ ^
^
31 30
23 22
0
Figure 4 - Format of a Data Field in a Data Frame
