wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

41-2 Industrial Communication Systems
To external memory
MAC
processor
Network
processor
Appl.
processor
ROM
EEPROM
RAM
Address bus (16 bit)
Data bus (8 bit)
Control
Timer/
counter
Application I/O
Network
Com. Port
Reset Service
Clock
IO 0 ... 10
To application specific HW
CP 0 ... 4
To transceiver
FIGURE 41.1
Structure of a Neuron Chip.
As shown in Figure 41.1, the Neuron Chip implements a three-processor architecture with shared
memory, which includes the firmware ROM, an EEPROM for the user application program, and RAM.
Each of the three processors handles a certain task:
The media access control (MAC) processor sends and receives messages to and from the communication
medium with support of the transceiver, which handles the line coding for a specific medium.
Since many different transceiver types exist, a wide range of communication media can be used, such
as twisted pair, power line, fiber optics, and radio frequency. The network processor handles the upper
layers of the LonTalk protocol, which are described in the next section. And the application processor
runs the user application implementing the specific task of the node.
The communication among the three processors is realized in shared RAM by communication buffers
and flags. There are input and output buffer queues storing messages to be forwarded to the other
processors. Special flag bytes indicate that the other processor should do a certain action, such as creating,
sending, or receiving a message.
Peripheral hardware, such as sensors and actuators, are connected to a set of I/O pins, which can be
configured in a range of single bit input and output for switches or LEDs via nibble and byte input and
output up to higher I/O protocols, such as serial and parallel interfaces, I 2 C, and Magcard.
There are also alternatives to the Neuron Chip. For example, LOYTEC offers a more powerful ARM7-
based embedded controller (LC3020) that implements the LonTalk protocol according to CEA-709 as
well. It also supports LonWorks/IP (standardized as CEA-852 [8]), where LonTalk messages are tunneled
over LAN or Internet in IP packets. Such controllers are used for more complex tasks, like panels
with a graphical user interface or IP routers.
To identify the LonWorks nodes in the network, each Neuron Chip has a fixed 48 bit identifier called
Neuron ID assigned by the manufacturer. A LonWorks node can actively transmit its Neuron ID in a
service pin message, when a special service pin is pressed on the node. This simplifies the network integration,
when new nodes have to be added to the network, because it is not required to enter the Neuron
ID manually in the management tool. Instead, the management tool simply has to wait for the service
pin message.
During configuration, a logical address is assigned to each node. It consists of the domain, subnet,
and node ID. The domain represents a whole LonWorks network, which is identified by the domain ID
with up to 6 bytes length. Direct message passing among domains is not possible, but it can be done via
gateways.
© 2011 by Taylor and Francis Group, LLC