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Title: DL405 Interrupt Input Module

Manual Number: D4–INTR–M

Issue Date Effective Pages Description of Changes

Original 8/94 Cover/Copyright

Contents

Manual History

1 — 24

Original Issue

Rev. A 6/98 Entire Manual

Manual Revisions Downsize to spiral

Rev. A

Table of Contents

Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Overview of the module’s operation 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Module Features 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Interrupt Signal Processing 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

When do you need an interrupt? 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

How does an interrupt solve response problems? 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

How does the CPU process the interrupts? 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Special Considerations in CPU processing 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Do I have to use an Interrupt Module? 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

What can I use in the Interrupt routines? 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

When can the Interrupts Occur? 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Using the Interrupt Input Module...4 Steps 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Physical layout of the D4–INT components 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Step 1: Setting the DIP Switches 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Switch 1: Enabling/Disabling Input Points 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Switch 2: Selecting Rising or Falling Edge Triggering 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Switch 2: Selecting the Response Delay Time 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Step 2: Installing the Module in the Base 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Module Restrictions 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CPU Compatibility 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Installing the Module in the Base 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

I/O Points Used 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

I/O Assignments with a D4–430 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

I/O Assignments with a D4–440 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Step 3: Connecting the Field Wiring 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Wiring Guidelines 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Typical Field Wiring and Internal Module Wiring 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Solid State Field Device Wiring 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Check the Terminal Block 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Step 4: Writing the Control Program 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Task 1: Enable / Disable the Interrupts 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Task 2: Place Numbered Interrupt Subroutines after the END Statement 20. . . . . . . . . . . . . . . . . .

Task 3: Understand the Types of Instructions used in Interrupt Subroutines 21. . . . . . . . . . . . . . . .

Task 4: Enter the Conditions for a Return from the Subroutine 22. . . . . . . . . . . . . . . . . . . . . . . . . . . .

Troubleshooting 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Specifications 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Environmental Specifications 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Operating Specifications 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

111

Introduction

The DL405 Interrupt Input module (D4–INT) is

an 8-point isolated interrupt input module for

use with the DL405 family of products. The

module consumes 16 X input points and must

be installed in Slot 0, next to the CPU. You can

use two Interrupt modules, installed in Slots 0

and 1, if you are using a D4–440 CPU. (More

on this later.)

The Interrupt module is intended for applications

that have one or more high-priority events which

require immediate attention. That is, these are

events that cannot wait until the CPU has

finished it’s normal program execution.

When this high priority event occurs, the

interrupt module sends an interrupt signal to the

CPU. Once the interrupt is received, the CPU

immediately suspends its routine scan cycle

and jumps to a subroutine that corresponds to

the particular interrupt input signal.

The following diagram shows a brief overview of this concept.

Main Program

Interrupt

Subroutine(s)

1. Field device (event) triggers

an interrupt signal from the

interrupt module to the CPU.

2. CPU recognizes the interrupt, stops the

normal program execution, and jumps to

subroutine.

END Statement 3. CPU finishes the subroutine

executionandreturnstothepoint

where it left in the normal

program execution.

This module has some great features that make interrupt processing easier.

SInterrupts are prioritized (lowest number takes priority)

SRising or Falling edge trigger

SSelectable response delay (allows you to easily ignore false signals)

SModule parameters are easily selected by setting dipswitches on the

back of the module

SNo complex programming, only simple ladder instructions are required

SIf you don’t use all 8 points as interrupts, you can use the non-interrupt

points as regular discrete inputs.

Overview of the

module’s operation

Module Features

Interrupt Signal Processing

In normal circumstances, the CPU reads the status of input points, solves the relay

logic program, and then updates all of the output points. This process is called the

scan and usually takes place in a matter of milliseconds. The following diagram

shows how this works.

Solve

Program

Read

Inputs

Write

Outputs

Scan

Critical Event

Input Module

Off/On Delay

Output Module

Off/On Delay

Normal Scan

Solve

Program

Output Turns

Solve

Program

Event occurs in the middle of the

program execution

Longer Overall

Response Time

As you can see from the diagram, there can be a delay between the actual

occurrenceoftheeventandtheCPUprocessingrequiredtorespondtotheevent.In

mostapplications,thescanhappensdozensoftimesinasecond,sothedelayisnot

critical.

However, in some applications you can have events that require an immediate

response. For example, your application may have a critical event that requires an

action to be initiated within 10 milliseconds of when the event occurs. Even with a

veryfastscantime,itmaytake10to30millisecondstocompletelyscantheprogram

before it can update any outputs. So, you can see that you need some method for

interrupting the normal scan to react to these critical events.

When do you need

an interrupt?

333

What is needed is a mechanism for

interrupting

the normal CPU scan cycle when

something needs to be done. The CPU can then take care of what has to be done,

and go back to its normal business. Here is the same diagram, but it has been

changedtoshowhowtheCPUreactsiftheCriticalFieldEventisbeingmonitoredby

an Interrupt Input Module. There are several things to notice.

SThere is very little Off/On delay (the Interrupt Module has selectable

response, or filtering).

SWhen an interrupt is received, two things happen.

1. The CPU

finishes executing the current program rung

2. The CPU then suspends the normal program execution and jumps to

a subroutine that corresponds to the interrupt point that became active.

SBy using Immediate Instructions in the Subroutine, you can quickly read

input points and write output points.

SThe CPU resumes the normal program execution on the rung

following

the rung that was being processed when the interrupt occurred.

Interrupt

Module

Off/On Delay

Sol

Prog

ram

Solve

Program

Return to

point in program where

interrupt occurred

Scan

Critical Event

Output Module

Off/On Delay

Shorter Overall Response Time

Normal Scan

Solve

Program

Use Immediate Output in the Interrupt

Subroutine to turn output on before the

end of the normal scan

Event occurs in the middle of the

program execution

Execute

Subroutine

Interrupt Module has

selectable filtering for

shorter response delays

Read

Inputs

Write

Outputs

How does an

interrupt solve

response

problems?

ItmayhelpyoutounderstandexactlyhowtheCPUworkstogetherwiththeInterrupt

module to process the interrupt signals.

Single Interrupt Signal: When the interrupt input module senses an input signal, it

has an extremely short delay before it signals an interrupt. This

Response Delay

(also called filtering) can be selected via a dipswitch setting and helps reduce the

possibility of false interrupt signals. (The Response Delay ranges are discussed in

more detail later in this manual.)

Once the delay period has passed, the module will latch an internal signal and send

aninterrupt requestto theCPU. OncetheCPU receivesthe request,theCPU stops

itsnormalscantojumpintotheinterruptroutine;andatthesametime,sendsareset

signal back to the module. The following diagram shows this operation.

Input signal (X0)

Latch output

CPU resets latch

<0.08ms

0.16ms

0.5ms

Latch

This sig al ig ored,

duratio is less tha

respo se delay selectio

OffĆtoĆO delay expires, sig al is ot false. Module latches

sig al for 0.5ms, se ds i terrupt request to the CPU.

Execute

i terrupt

subrouti e 0

I terrupt

Mai

Program

Internal CPU

processing Back to

Mai

Program

Multiple Signals from the Same Interrupt Input: There may be occasions where

several interrupt signals are received very close together in time. In the diagram

below, the time line reads from left to right. The first signal is latched. It takes 0.5

millisecondstocompletethelatchingprocess.Ifwithinthattimespananothersignal

is sent, the module will ignore the second signal and only recognize the first.

Execute

i terrupt

subrouti e 0

I terrupt

Mai

Program

Internal CPU

processing Back to

Mai

Program

Input signal (X0)

Latch output

CPU resets latch

0.16ms

0.5ms

Latch

This sig al ig ored,

occurred while i terrupt

poi t was bei g latched.

0.16ms

Respo se delay

expires, latch sig al

How does the CPU

process the

interrupts?

555

Simultaneous Signals from

Different

Interrupt Inputs: What happens if the

module senses signals simultaneously from several of the interrupt input points? In

this case, there is a priority. The highest priority is given to X0, then comes X1, then

X2 and so forth down to X7. The diagram below shows two signals being received

simultaneously.

Execute

interrupt

subroutine 0

Input signal (X0)

Latch interrupt

request 0

Reset latch 0

Input signal (X1)

Reset latch 1

Interrupt

Main Program

Internal CPU

processing

Latch interrupt

request 1

Back to Main

Program

Execute

interrupt

subroutine 1

(Example assumes that signals are true, and does not show response delay)

In each of the previous examples, you noticed that the CPU interrupted the main

program execution. The CPU does not just drop everything that it is doing. Instead,

the CPU performs an orderly transition to the subroutine by

finishing the current

programrungbefore it jumpstothesubroutine.

Thistypicallytakes atleast 1ms,but

the actual response depends on the instructions on the rung. For example, if the

CPU receives the interrupt signal on a rung that contains several math instructions,

then the response will be slower than if the rung only contained a simple output coil.

There’s not much you can do about this, but just be aware of it.

Also, since the CPU only executes the logic in the interrupt subroutine, it does not

handle any communication requests from external devices. In the vast majority of

casesthisisnotaproblem.However,someoperatorinterfacescanhavea“timeout”

type of error if they issue a request and do not get a response from the CPU in a

certain amount of time. If you are using an Operator Interface and this happens, try

reducing the communications baud rate. The slower speeds usually allow for a

longer response time from the CPU.

Special

Considerations in

CPU processing

You don’t always have to use an Interrupt Input module to generate an interrupt.

Basically, an interrupt can be initiated two different ways:

SYou can use a timed interrupt (an interrupt on a defined time interval,

D4–440 CPU only)

SOr, you can use the Interrupt Input module (interrupt triggered by a limit

switch closing, proximity switch, etc. via the interrupt module)

NOTE: Theseexamples DO NOT show all oftheinstructionsnecessary to correctly

program an interrupt routine. This is discussed later in this manual.

Timed Interrupts: The D4–440 offers a

single timed interrupt

instruction

. You can

specify how often the interrupt occurs,

from 3–1000 ms. This is great for those

applications where you know you need to

takesomeactioneverysooften.However,

itmayalsoslowthesystemdownbecause

it may be executing even when the

machine (or process) doesn’t need

immediate attention.

NOTE: The time value is specified in

BCD format. If the number is not BCD,

or if the number is outside of the range

(3–1000) then the routine will not work.

You may have noticed that we didn’t

mentionthe D4–430. Timed Interrupts are

not available in the D4–430.

INT O 17

END

OUTI

X20

LD K10

Load the constant, K10,

which will indicate 10

milliseconds

OUT V737

Copy the value to V737, which

is used to define the time inter-

val for the timed interrupt

Interrupt happens

every 10ms in

this example

Hardware Interrupts: In the vast majority of

applications, there is some real world event,

such as a switch closing, etc. that needs to

trigger an interrupt. By wiring these field

devices to an Interrupt Input module, you

can easily interrupt the CPU scan cycle

when the event occurs. INT O 1

END

OUTI

X20

INT O 2

OUTI

X21

Whenthe interrupt inputpointcomes on,

the CPU suspends the normal program

execution and jumps to the interrupt

routine that corresponds to the interrupt

point, X0 – Interrupt 0, X1 – Interrupt 1,

etc. Once the subroutine execution is

complete, the CPU returns to the main

program.

In the example shown here, the CPU

automatically handles the transition to

the Interrupt subroutine whenever

Interrupt input X1 comes on.

(Main program)

Executes routine

and returns to the

main program

IRT

Do I have to use an

Interrupt Module?

777

X20

In any of the above methods, Interrupt

subroutines are required. These subroutines

are placed

after

the END statement, which is

the last line in the main program.

INT O 1

END

OUTI

X21

INT O 2

Y20

OUTI

X40

(Main Program)

You can use most any type of instruction

in the subroutines. You can have math

instructions, data manipulation

instructions, etc. However, most people

find that the Immediate instructions and

the FOR/NEXT looping instructions are

the most useful. Immediate instructions

immediately read the status of inputs

and/or immediately update the outputs.

Byusingtheimmediateinstructionsinthe

subroutine, the CPU can read input

points or update output points

immediately. By using the FOR/NEXT

instructions, you can literally have a

“mini-scan” by creating a loop inside of

the subroutine.

FOR

OUTI

X22

OUTI

X23

123

(Loops 3 times before

returning to program)

IRT

NOTE:Youcanuse manydifferenttypesof instructionsinthe interruptsubroutines.

However, if you use instructions with long execution times, such as some math

instructions,FOR/NEXTloops,etc.,thenyoumayexceedtheWatchdogTimerlimit.

The Watchdog Timer is set at 200ms from the factory. It can be changed with the

handheldprogrammeror

Direct

SOFT.YoucanalsouseaRSTWTinstructioninside

of the subroutine to reset the Watchdog Timer.

ThepreviousdiagramsshowedasimplifiedCPUscancycle.However,theCPUcan

process the interrupts during any portion of the scan cycle. Interrupts can occur in

themiddleofthecommunicationsservice,inputupdate,outputupdate,etc.So,this

helps ensure the fastest possible response for critical events.

The CPU does not perform any other functions when it is executing the interrupt

subroutine. For example, the CPU will not acknowledge any communication

requestsuntilithasfinishedwiththeinterruptsubroutine.Somedevices,suchasan

operatorinterface,mayissueacommunicationstimeouterrorduetothe delayinthe

response from the CPU. If this occurs, check your device documentation for

procedures on changing the communications timeout error settings.

Now that you understand how the CPU processes the Interrupts, you’re ready to

install (and use) the D4–INT Interrupt module.

What can I use in

the Interrupt

routines?

When can the

Interrupts Occur?

Using the Interrupt Input Module..4 easy steps!

Yes, I know, you were expecting to see the “4 Steps” on this page. But, first, take a

minute and familiarize yourself with the basic physical characteristics. It will make

the “4 Steps” even easier.

SThe dipswitches are located on the back of the module.

SThe terminal block can be easily removed by loosening the terminal

block retaining screws.

SThe LED status indicators show you when an input is active.

Base Connector

DIP Switches for response

time, trigger direction &

enable/disable

Status Indicators

Removable

Terminal Block

INTERRUPT MDOULE

Front Back

D4-INT

Physical layout of

the D4–INT

components

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