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Upgrading Existing Series 500 Installations

C-17

SIMATIC 545/555/575 System Manual

The base thumbwheel shown in Figure C-7 is used to reset the Series 500

RBC during system operation and to assign the base address.

WARNING

If you reset the RBC when the system is operating, the RBC is logged off the

system. When the RBC is logged off, inputs and outputs associated with the

base are affected, as described below. If you do not take the condition of your

inputs and outputs into account, logging the RBC off the system can cause

unpredictable process operation.

Unpredictable process operation can cause death or serious injury to

personnel, and/or damage to equipment.

Do not reset your RBC unless you understand and are prepared for the

consequences (described below).

If you want to use the base thumbwheel switch to reset the Series 500 RBC

while the system is operating, momentarily change the switch to another

number, then quickly return it to the correct base address setting.

The following actions take place when an RBC is reset.

• The CPU logs the RBC off the system and zeros the image register

points which represent the inputs from this RBC’s base. The image

communication with the CPU. If this occurs while the system is

operating, depending on your RLL program, turning these inputs off

could affect other base outputs.

• From the assertion of reset until the RBC completes the reset and

resumes communication with the CPU, the state of the outputs on this

RBC’s base is determined by the output module, with no reference to

the RBC’s Off/Freeze switch. Discrete outputs go off (to a value of zero).

Analog/word outputs obey their own Zero/Hold Last Value selection. If

no Zero/Hold Last Value selection is available on the module, the

analog/word outputs hold their last value.

• If the base number you assign to the RBC (by setting the base

thumbwheel) inadvertently duplicates the number already in use by a

second RBC on the I/O channel, when the first RBC completes its reset

and attempts to communicate, identifying itself with the new base

number, the second RBC will be logged off the system. The state of the

second RBC’s outputs is determined by the selection made on the RBC’s

Off/Freeze switch. The CPU image register containing the input points

for the second RBC is zeroed. Intermittent operation could occur as

long as the two RBC base thumbwheels are set to the same number.

Using the Base

Thumbwheel

Resetting the RBC

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