COM20051 Datasheet, PDF (48/82 Pages) List of Unclassifed Manufacturers – Integrated Microcontroller and ARCNET (ANSI 878.1) Interface

COM20051 APPLICATIONS INFORMATION
PROGRAMMING THE COM20051 NETWORK
CORE
The COM20051 ARCNET core is relatively
simple to program. The ARCNET core was
designed to allow the processor to remain in
control of the node and to perform network flow
control with a minimum of processor intervention.
There are two methods of operating the
ARCNET core: in Command Chaining and Non-
Command Chaining mode. Command chaining
mode permits the processor to pipeline up to two
transmit and two receive commands. In normal
Non-Command Chaining mode, the
microcontroller must access the ARCNET core
for each individual transmission and reception
since the ARCNET core can only handle one
transmit and one receive command at any given
time. The Command Chaining mode permits the
ARCNET core to handle up to two transmit and
two receive commands at any given time.
Receive and Transmit status bits are buffered for
each command in Command Chaining mode.
2) Configuring the Operating Mode (Command
or Non-Command Chaining, Backplane or
Dipulse operation)
3) Programming the Interrupt Routing Register
(IRR)
4) Programming the Data Rate (optional)
5) Enabling the Receive All mode (optional)
6) Obtaining a Node ID and programming in its
value
7) Entering the Network
8) Issuing initial Receive commands
Figure 14 is a flowchart of a typical initialization
procedure.
Steps 1 through 5 are
straightforward and do not require much
explanation. Step 6, Selection of a Node ID can
be somewhat more involved depending on the
application. There are many methods of
obtaining a unique node id for a particular node
ranging from simply reading a switch to
sophisticated software algorithms. Several
methods will be discussed but the best method
depends on the particular application.
The basic software approach can be divided into
three parts: ARCNET initialization, Transmit
Interrupt servicing, and Receive Interrupt
servicing. Both Command and Non-Command
Chaining examples will be illustrated. It is
strongly suggested that an interrupt driven
approach be used since polling methods can
result in lost transmit opportunities and in lost
receptions.
ARCNET Initialization
Basic COM20051 ARCNET core initialization
consists of the following:
1) Programming of the Address Decode
Register
Node ID Selection
The ARCNET Protocol is a token passing
protocol that relies on each station to have a
unique Node ID in order to permit proper network
operation. Many methods will be discussed but it
is up to the user to choose the right method for
his application.
Method 1 - Hardware Switch Read
This is the simplest and the most common form
of obtaining a Node ID for an individual node. It
consists of adding an eight bit DIP switch and
address decoder as shown in Figure 15. A
simple read from the microcontroller will obtain
the ID value.
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