Connecting the System
3–17
Establishing Communication
When you connect a MicroLogix 1000 controller to a network, it automatically
finds which protocol is active (DF1 or DH-485), and establishes communication
accordingly. Therefore, no special configuration is required to connect to either
network.
However, to shorten the connection time, you can specify which protocol the
controller should attempt to establish communication with first. This is done using
the Primary Protocol bit, S:0/10. The default setting for this bit is DF1 (0). If the
primary protocol bit is set to DF1, the MicroLogix 1000 controller will attempt to
connect using the configured DF1 protocol; either full-duplex or half-duplex slave.
To have the controller first attempt DH-485 communication, set this bit to 1.
For DH-485 networks that will only contain MicroLogix controllers, at least one
controller must have its primary protocol bit set to 1 so that the network can be
initialized.
Automatic Protocol Switching
The MicroLogix 1000 Series D or later discrete and all MicroLogix 1000 analog
controllers perform automatic protocol switching between DH-485 and the
configured DF1 protocol. (The controller cannot automatically switch between DF1
full-duplex and DF1 half-duplex slave.) This feature allows you to switch from
active communication on a DF1 half-duplex network to the DH-485 protocol to
make program changes.
Simply disconnect the MicroLogix controller from the DF1 half-duplex network and
connect it to your personal computer. The controller recognizes the computer is
attempting to communicate using the DH-485 protocol and automatically switches
to it. When your program changes are complete, you can disconnect your computer,
reconnect the modem, and the controller automatically switches back to the
configured DF1 protocol. For example, if you are using the DH-485 protocol to
make program changes and you connect an HHP
, you can switch to active
communication on a DF1 full-duplex network.
The following baud rate limitations affect autoswitching:
• If the configured DH-485 baud rate is 19200, the configured DF1 baud rate
must be 4800 or greater.
• If the configured DH-485 baud rate is 9600, the configured DF1 baud rate must
be 2400 or greater.
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