Page 213 - Programmable Logic Controllers, Fifth Edition - Mobile version

IIM IOM SYC MSG IIE IID RPI REF
Read inputs
11 11 00 Input/Output Compare Compute/Math Move/Logic
00 00 10
00 00 01
IOM
I/O Data files Write inputs
Immediate Output w/ Mask
Immediate output
Slot O:4.0
Mask 0FFFh
Immediate input Length 2
Program
logic scan Figure 9-16 Immediate output with mask (IOM) instruction.

Figure 9-14 Immediate I/O instructions.
The immediate output with mask (IOM) instruction
is shown in Figure 9-16. The IOM operates on the
to the commands in the ladder following the IIM in- physical outputs assigned to a particular word of a
struction. The following parameters are entered in the slot. When the IOM rung is true, the program scan
instruction: is interrupted to update output data to the module lo-
Slot Specifies the slot and word that contain the data cated in the slot specified in the instruction. These
to be updated. For example, I:3.0 means the input of data are then available to the commands in the lad-
slot 3, word 0. der following the IOM instruction. The parameters
Mask Specifies either a hex constant or a register entered are basically the same as those entered for the
address. For the mask, a 1 in the bit position passes IIM instruction.
data from the source to the destination. A 0 inhibits Processor communication with the local chassis is
or blocks bits from passing from the source to the many times faster than communication with the remote
destination. chassis. This is due to the fact that local I/O scan is
synchronous with the program scan and communication
Length Used to transfer more than one word per is in parallel with the processor, whereas the remote
slot. I/O scan is asynchronous with the program scan and

The program operation of the instruction is summarized communication with remote I/O is serial. For this rea-
as follows: son, fast-acting devices should be wired into the local
chassis.
• The IIM instruction retrieves data from I:1.0 and ControlLogix PLCs have no immediate input instruc-
passes it through the mask. tion as they use asynchronous I/O control compared to the
• The mask permits only the four least significant bits SLC 500 controllers which use synchronous I/O control.
to be moved to the input register I:1.0. ControlLogix controllers do have an immediate output
• This allows the programmer to update only sections (IOT) instruction, which operates the same as the immedi-
of the inputs to be used throughout the rest of the ate output instruction for the SLC 500. Figure 9-17 shows
program. an example of the IOT instruction. In this example, when
the IOT instruction executes, it immediately updates the
entire output module Local:3:0. When you use the in-
struction to update the output card, address the entire card
IIM IOM SYC MSG IIE IID RPI REF
(Local:3:0), and not the individual outputs (Local:3:0.
Input/Output Compare Compute/Math Move/Logic Data 0).

IIM
Immediate Input w/ Mask
Label_Sensor
Slot I:1.0 Label_Sensor IOT
Mask 000Fh Immediate output
Length 1 Update tag Local:3:0

Figure 9-15 Immediate input with mask (IIM) instruction. Figure 9-17 ControlLogix immediate output instruction.

194 Chapter 9 Program Control Instructions

pet73842_ch09_184-206.indd 194 03/11/15 4:01 PM