COM20051I Datasheet, PDF (43/74 Pages) SMSC Corporation – Integrated Microcontroller and ARCNET (ANSI 878.1) Interface

COM20051I APPLICATIONS INFORMATION
PROGRAMMING THE COM20051I NETWORK CORE
The COM20051I 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.
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 COM20051I ARCNET core initialization consists of the following:
1) Programming of the Address Decode Register
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.
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.
SMSC DS – COM20051I
Page 43
Rev. 03/27/2000