Auto-Zone Control Systems Auto-Zone CV & CV-EX Systems Installation & Operation (Version 01C) - Manual (Page 79)

Auto-Zone CV & CV-EX
Section 4
Start-Up and Troubleshooting 4-1
Communications
Overview
Perhaps no other portion of the system seems as difficult to diagnose as the communica-
tions loop, yet it really can be quite simple if you understand how it works. In fact, much
of the troubleshooting can be done by simple observation. We will lead you through the
system functions and then provide you with detailed instructions for checking each piece
of equipment.
How It Works
Auto-Zone uses a token-passing loop architecture, which means in simple terms that an
“electronic message” called a token is passed from controller to controller in a round-
robin fashion. A controller must wait to receive the token before it can send or request
any data. Only one device on each loop is capable of sending the token, and this device is
considered the loop master. The loop master varies depending on the type of system and
the installed options. For the CV system, the loop master is the CommLink. The
CommLink must be connected to the system or the communications will not function. For
the CV-EX system, the Local Loop master for the CV controllers is the MiniLink, and the
Network Loop master is the CommLink.
Note: It is very important to know which device is the loop master on the loop you are
troubleshooting.
In order for the loop master to communicate with the various devices on that loop, each
must have a unique address. With the CV or CV-EX system, each CV controller on the
local loop must have its own address from 1 to 30. For the CV system, this is all that is
required. For the CV-EX system, in addition to each CV controller being addressed, the
MiniLink on each local loop must have its own unique address between 1 and 4. Please
see Figure 4-5 for address switch setting information.