1766-RM001A-EN-P MicroLogix 1400 Programmable Controllers ...

Programming Instructions Overview 93Addressing ModesThe MicroLogix 1400 supports three types of data addressing:• Immediate• Direct• IndirectThe MicroLogix 1400 do not support indexed addressing. Indexedaddressing can be duplicated with indirect addressing. See Example -Using Indirect Addressing to Duplicate Indexed Addressing on page 97.How or when each type is used depends on the instruction beingprogrammed and the type of elements specified within the operands ofthe instruction. By supporting these three addressing methods, theMicroLogix 1400 allows incredible flexibility in how data can bemonitored or manipulated. Each of the addressing modes are describedbelow.Immediate AddressingImmediate addressing is primarily used to assign numeric constants withininstructions. For example: You require a 10 second timer, so you programa timer with a 1 second time base and a preset value of 10. The numbers1 and 10 in this example are both forms of immediate addressing.Direct AddressingWhen you use direct addressing, you define a specific data location withinthe controller. Any data location that is supported by the elements of anoperand within the instruction being programmed can be used. In thisexample we are illustrating a limit instruction, where:• Low Limit = Numeric value (from -32,768…32,767) enteredfrom the programming software.• Test Value = LCD:0.POT0 (This is the current position/value oftrim pot 0.)• High Limit = N7:17 (This is the data resident in Integer file 7,element 17.)The Test Value (LCD:0.POT0) and High Limit (N7:17) are directaddressing examples. The Low Limit is immediate addressing.Publication 1766-RM001A-EN-P - October 2008