Bradley Smoker PLC-5 Specifying Indexed Addresses, Value Base Address, Source N710 N720

4-20Addressing I/O and Controller Memory

Specifying Indexed Addresses

The controller starts operation at the base address plus the offset. Store the offset value in the offset word in the controller’s status file. You can manipulate the offset word in your ladder logic.

The indexed address symbol is the # character. Place the # character immediately before the file-type identifier in a logical address. Enter the offset value in the status file S:24. All indexed instructions use S:24 to store an offset.

When you specify indexed addresses, follow these guidelines:

•Make sure the index value (positive or negative) does not cause the indexed address to exceed the file-type boundary.

ATTENTION

The controller does not check indexed addresses to make sure that the addresses do not cross data-table file boundaries (e.g., N7 to F8). You could even modify the status file, which is physically the last data table file. But if the indexed address exceeds the data-table area of memory, the controller initiates a run-time error and sets a major fault.

•When an instruction uses more than two indexed addresses, the controller uses the same index value for each indexed address.

•Set the offset word to the index value you want immediately before enabling an instruction that uses an indexed address.

ATTENTION

Instructions with a # sign in an address manipulate the offset value stored at S:24. Make sure you monitor or load the offset value you want prior to using an indexed address. Otherwise unpredictable machine operation could occur with possible damage to equipment and/or injury to personnel.

MVM

MASKED MOVE

Source#N7:10

Mask00110011

Destination #N11:5

The following MVM example uses an indexed address in the source and destination addresses. If the offset value is 10 (stored in S:24), the controller manipulates the data stored at the base address plus the offset.

Value	Base Address	Offset Address
Source	N7:10	N7:20
Destination	N11:5	N11:15

Publication 1785-UM012D-EN-P - July 2005