Chapter 7 - AutomationDirect
Contents
1. DL205 User Manual 4th Edition Rev B 7 27 Chapter 7 RLL Stage Programming a In this example the Block Call is executed when DiecBoFT stage 1 is active and X6 is on The Block Call then z automatically activates stage S10 which s1 immediately follows the Block instruction A Y5 This allows the stages between S10 and the Block OUT End instruction to operate as programmed If the X6 is y a BCALL instruction is turned off or if the stage containing the BCALL instruction is turned off BLK then all stages between the BLK and BEND co instructions are automatically turned off ae If you examine 15 you will notice that X7 could Ye X3 reset Stage S1 which would disable the BCALL i or thus resetting all stages within the block BEND Handheld Programmer Keystrokes SG gt s 1 ENT SG Sik STR gt xm 2 ENT Ra st OUT gt Youn 5 ENT L c RST STR gt X IN 6 ENT SHFT B Cc A L L gt cer 0 ENT SHFT B L K gt C CR 0 ENT SG gt see 1 0 ENT STR gt X IN 3 ENT OUT gt Y OUT 6 ENT SHFT B E N D ENT SG gt T se 1 5 ENT STR gt X IN 7 ENT RST gt S SG 1 ENT Stage View in DirectSOFT The Stage View option2. is closed The motor has two command inputs raise and lower When neither input is active the motor is stopped e lt Door Command The door command is a simple pushbutton Whether wall mounted as shown or a radio remote control all door control commands logically OR together as one Down limit switch pair of switch contacts Draw the Block Diagram The block diagram of the controller is shown to the right Input XO is from the pushbutton door control Inputs Outputs Input X1 energizes when the door reaches the full up Toggle position Input X2 energizes when the door reaches o oS the full down position When the door is positioned aini Ladder pee ae j p limit P between fully up or down both limit switches are rogram y l 0 0 m gt Raise open The controller has two outputs to drive the motor Downiumit x2 y2 h 0 0 a gt Lower Y1 is the up raise the door command and Y2 is the down lower the door command 7 10 DL205 User Manual 4th Edition Rev B Chapter 7 RLL Stage Programming Draw the State Diagram Now we are ready to draw the state transition diagram Like the previous light bulb controller example this application also has only one switch for the command input Refer to the figure below e When the door is down DOWN state nothing happens until XO energizes Its push and release brings us to the RAISE state where output Y1 turns on and causes
3. Block 0 Block 1 Block 2 Doo ee ee Stages outside blocks niles HOOD A program with 20 or more stages may be considered large enough to use block grouping however their use is not mandatory When used the number of stage blocks should probably be two or higher because the use of one block provides a negligible advantage A block of stages is separated from other ladder logic with special beginning and ending instructions In the figure to the right the BLK BEKS Block Instruction instruction at the top marks the start of the stage block At the bottom the Block End BEND marks the end of the block The stages in between Pay these boundary markers SO and S1 in this case and their associated rungs make up the block PT Note the block instruction has a reference value SG field set to C0 in the example The block instruction borrows or uses a control relay contact _All other rungs in stage number so that other parts of the program can Block End control the block Any control relay number such as Instruction TA i BEND C0 used in a BLK instruction is not available for use as a control relay penete NOTE The stages within a block must be regular stages SG or convergence stages CV So they cannot be initial stages The numbering of stages inside stage blocks can be in any order and is completely independent fr
4. Instead we give priority to the obstruction by changing the transition condition to the DOWN state to X2 AND NOT X3 This ensures the obstruction event has the priority The modifications we must make to the LOWER Stage S5 logic are shown to the right The first rung remains unchanged The second and third rungs implement the transitions we need Note the opposite relay contact usage for X3 which ensures the stage will execute only one of the JMP instructions 7 14 DL205 User Manual 4th Edition Rev B SG S5 LOWER State SP1 Y2 OUT x2 x3 to DOWN so 1 Qm X3 to Push UP S2 ump Chapter 7 RLL Stage Programming a Stage Program Design Considerations Stage Program Organization The examples so far in this chapter used one self contained state diagram to represent the main process However we can have multiple processes implemented in stages all in the same ladder program New stage programmers sometimes try to turn a stage on and off each scan based on the false assumption that only one stage can be on at a time For ladder rungs that you want to execute each scan put them in a stage that is always on The following figure shows a typical application During operation the primary manufacturing activity Main Process Powerup Initialization E Stop and Alarm Monitoring and Operator Interface are all running At powerup four initial stages shown begin operation Main Pr
5. e Any rung in the program can execute a Reset Stage Bit instruction such as RST S0 Q What about the power flow technique of stage transitions A The power flow method of connecting adjacent stages directly above or below in the program actually is the same as the Stage Jump instruction executed in the stage above naming the stage below Power flow transitions are more difficult to edit in DirectSOFT we list them separately from two preceding questions DL205 User Manual 4th Edition Rev B 7 29 Chapter 7 RLL Stage Programming Q Can I have a stage which is active for only one scan A Yes but this is not the intended use for a stage Instead make a ladder rung active for one scan by including a stage Jump instruction at the bottom of the rung Then the ladder will execute on the last scan before its stage jumps to a new one Q Isnt a Stage JMP just like a regular GOTO instruction used in software A No it is very different A GOTO instruction sends the program execution immediately to the code location named by the GOTO A Stage JMP simply resets the Stage Bit of the current stage while setting the Stage Bit of the stage named in the JMP instruction Stage bits are 0 or 1 determining the inactive active status of the corresponding stages A stage JMP has the following results e When the JMP is executed the remainder of the current stage s rungs are executed even if they reside past under the JMP instructio
6. x2 so mp SG S6 LIGHT State SP1 Y3 i A ouT TMR TO K1800 TO S6 1 Rs DL205 User Manual 4th Edition Rev B 7 13 Chapter 7 RLL Stage Programming Add Emergency Stop Feature Some garage door openers today will detect an object under the door This halts further lowering of the door Usually implemented with a photocell electric eye a door in the process of being lowered will halt and begin raising We will define our safety feature to work in this way adding the input from the photocell to the block diagram as shown to the right X3 will be on if an object is in the path of the door Next we make a simple addition to the state transition diagram shown in shaded areas in the figure below Note the new transition path at the top of the LOWER state If we are lowering the door and detect an obstruction X3 we then jump to the Push UP State We do this instead of jumping directly to the RAISE state to give the Lower output Y2 one scan to turn off before the Raise output Y1 energizes cS Inputs Outputs Toggle Y1 o oO Raise Up limit so Ladder 2 Lower Down limit Program o ol RENS Light Obstruction ol Exclusive Transitions It is theoretically possible the down limit X2 and the obstruction input X3 could energize at the same moment In that case we would jump to the Push UP and DOWN states simultaneously which does not make sense
7. This continues until the 5 door reaches the down limit switch X2 When X2 closes we SP1 Y2 transition from Stage S5 to the DOWN stage S0 where we began out S x2 so NOTE The only thing special about an initial stage ISG is that it is UMP automatically active at powerup Afterwards it is just like any other DL205 User Manual 4th Edition Rev B 7 11 Chapter 7 RLL Stage Programming Add Safety Light Feature Next we will add a safety light feature to the door opener system It s best to get the main function working first as we have done then adding the secondary features The safety light is standard on many commercially available garage door openers It is shown to the right mounted on the motor housing The light turns on upon any door activity remaining on for approximately 3 minutes afterwards This part of the exercise will demonstrate the use of parallel states in our state diagram Instead of using the JMP instruction we will use the set and reset commands Modify the Block Diagram and State Diagram To control the light bulb we add an output to our controller block diagram shown to the right Y3 is the light control output In the diagram below we add an additional state called LIGHT Whenever the garage owner presses the door control switch and releases the RAISE or LOWER state is active and the LIGHT state is simultaneously active The line to the Light state is dashed b
8. e The convergence jump CVJMP is the intended method to be used to transition from the convergence group of stages to the next stage The CVJMP resets all convergence stages of the group and energizes the stage named in the jump e The CVJMP instruction must only be used in a convergence stage as it is invalid in regular or initial stages e Convergence Stages or CVJMP instructions may not be used in subroutines or interrupt routines 7 20 DL205 User Manual 4th Edition Rev B Chapter 7 RLL Stage Programming i Managing Large Programs A stage may contain a lot of ladder rungs or only one or two program rungs For most applications good program design will ensure the average number of rungs per stage will be small However large application programs will still create a large number of stages We introduce a new construct which will help us organize related stages into groups called blocks So program organization is the main benefit of the use of stage blocks Stage Blocks BLK BEND A block is a section of ladder program which contains stages In the figure below each block 230 basi ast as its own reference number Like stages a stage block may be active or inactive Stages V 240 inside a block are not limited in how they may transition from one to another Note the use M 250 41 of stage blocks does not require each stage in a program to reside inside a block shown below 260 by the stages outside blocks
9. i Powerup Baa OFF State XO S1 o a Push On State Output equation YO ON xo 52 When in the ON state another push and release cycle VA CMP similarly takes us back to the OFF state Now we have two unique states OFF and ON used when the se ON State pushbutton is released which is what was required to Output solve the control problem SP1 Yo OUD The equivalent stage program is shown to the right The desired powerup state is OFF so we make S0 an initial a Pia stage ISG In the ON state we add special relay Gp contact SP1 which is always on oc 53 Push Off State Note that even as our programs grow more complex it is still easy to correlate the state transition diagram with XO SO the stage program M OMP 7 8 DL205 User Manual 4th Edition Rev B Chapter 7 RLL Stage Programming A Four Steps to Writing a Stage Program By now youve probably noticed that we follow the same steps to solve each example problem The steps will probably come to you automatically if you work through all the examples in this chapter It s helpful to have a checklist to guide us through the problem solving The following steps summarize the stage program design procedure 1 Write a Word Description of the application Describe all functions of the process in your own words Start by listing what happens first then next etc If you find there are too many things happening at once try dividing the problem into more th
10. transitions Q Isnt a stage really like a software subroutine A No it is very different A subroutine is called by a main program when needed and executes only once before returning to the point from which it was called A stage however is part of the main program It represents a state of the process so an active stage executes on every scan of the CPU until it becomes inactive Q What are Stage Bits 7 A A stage bit is a single bit in the CPU s image register representing the active inactive status of the stage in real time For example the bit for Stage 0 is referenced as SO If SO 0 then the ladder rungs in Stage 0 are bypassed not executed on each CPU scan If SO 1 then the ladder rungs in Stage 0 are executed on each CPU scan Stage bits when used as contacts allow one part of your program to monitor another part by detecting stage active inactive status Q How does a stage become active A There are three ways e If the Stage is an initial stage ISG it is automatically active at powerup e Another stage can execute a Stage JMP instruction naming this stage which makes it active upon its next occurrence in the program e A program rung can execute a Set Stage Bit instruction such as SET SO Q How does a stage become inactive A There are three ways e Standard Stages SG are automatically inactive at powerup e A stage can execute a Stage JMP instruction resetting its Stage Bit to 0
11. Reset the stages Control and Recipe E Stop and Alarm Monitoring DL205 User Manual 4th Edition Rev B 7 15 Chapter 7 RLL Stage Programming How Instructions Work Inside Stages We can think of states or stages as simply dividing up our ladder program as depicted in the figure below Each stage contains only the ladder rungs which are needed for the corresponding state of the process The logic for transitioning out of a stage is contained within that stage It s easy to choose which ladder rungs are active at powerup by using an initial stage type ISG Stage 2 Most instructions work like they do in standard RLL You can think of a stage like a miniature RLL program which is either active or inactive 7 Output Coils As expected output coils in active stages will turn on or off outputs according to power flow into the coil However note the following e Outputs work as usual provided each output reference such as Y3 is used in only one stage e Output coils automatically turn off when leaving a stage However Set and Reset instructions are not undone when leaving a stage e An output can be referenced from more than one stage as long as only one of the stages is active at a time e If an output coil is controlled by more than one stage simultaneously the active stage nearest the bottom of the program determines the final output status during each scan
12. So use the OROUT instruction instead when you want multiple stages to have a logical OR control of an output One Shot or PD coils Use care if you must use a Positive Differential coil in a stage Remember the input to the coil must make a 0 1 transition If the coil is already energized on the first scan when the stage becomes active the PD coil will not work This is because the 0 1 transition did not occur PD coil alternative If there is a task which you want to do only once on 1 scan it can be placed in a stage which transitions to the next stage on the same scan Counter When using a counter inside a stage the stage must be active for one scan before the input to the counter makes a 0 1 transition Otherwise there is no real transition and the counter will not count The ordinary Counter instruction does have a restriction inside stages it may not be reset from other stages using the RST instruction for the counter bit However the special Stage Counter provides a solution see next paragraph Stage Counter The Stage Counter has the benefit that its count may be globally reset from other stages by using the RST instruction It has a count input but no reset input This is the only difference from a standard counter instruction Drum Realize the drum sequencer is its own process and is a different programming method than stage programming If you need to use a drum and stages be sure to place the drum instruction
13. in DirectSOFT will let you view the ladder program as a flow chart The figure below shows the symbol convention used in the diagrams You may find the stage view useful as a tool to verify that your stage program has faithfully reproduced the logic of the state transition diagram you intend to realize SG Transition Stage Reference to i a Stage Logic gt Jump lt gt Set Stage QO Output R gt Reset Stage The following diagram is a typical stage view of a ladder program containing stages Note the left to right direction of the flow chart ISG i SG SG SG so 1 J S1 J 2 S4 SG SG O d 3 gt 5 7 28 DL205 User Manual 4th Edition Rev B Chapter 7 RLL Stage Programming Questions and Answers about Stage Programming We include the following commonly asked questions about Stage Programming as an aid to new students All question topics are covered in more detail in this chapter Q What does stage programming do that I can t do with regular RLL programs A Stages allow you to identify all the states of your process before you begin programming This approach is more organized because you divide up a ladder program into sections As stages these program sections are active only when they are actually needed by the process Most processes can be organized into a sequence of stages connected by event based
14. in an ISG stage that is always active 7 16 DL205 User Manual 4th Edition Rev B Chapter 7 RLL Stage Programming Using a Stage as a Supervisory Process You may recall the light bulb on off controller example from earlier in this chapter For the purpose i iy of illustration suppose we want to monitor the a a bs isa 58 Toggle Ladd productivity of the lamp process by counting the 5 oO adder Y0 number of on off cycles which occurs This Program application will require the addition of a simple counter but the key decision is in where to put the counter Powerup i OFF State Supervisor Process x0 1 Powerup New stage programming students will typically try to place the counter inside one of the stages of the process they are trying to monitor The problem with this approach is that the stage is active only part of the time In order for the counter to count the count input must transition from off to on at least one scan after its stage activates Ensuring this requires extra logic that can be tricky In this case we only need to add another supervisory stage as shown above to watch the main process The counter inside the supervisor stage uses the stage bit S1 of the main process as its count input Stage bits used as a contact let us monitor a process NOTE Both the Supervisor stage and the OFF stage are initial stages The supervisor stage remains active indefin
15. now let s assume we begin in the OFF State so sa stage SO is active When the On pushbutton X0 is S1 ON State pressed a stage transition occurs The JMP S1 Output instruction executes which simply turns off the Stage sp1 Always On Pu bit SO and turns on Stage bit S1 So on the next PLC oun scan the CPU will not execute Stage S0 but will e execute stage S1 zi Transition In the On State Stage S1 we want the motor to MP always be on The special relay contact SP1 is defined as always on so YO turns the motor on When the Off pushbutton X1 is pressed a transition back to the Off State occurs The JMP SO instruction executes which simply turns off the Stage bit S1 and turns on Stage bit SO On the next PLC scan the CPU will not execute Stage S1 so the motor output YO will turn off The Off state Stage 0 will be ready for the next cycle 7 4 DL205 User Manual 4th Edition Rev B Chapter 7 RLL Stage Programming Let s Compare Right now you may be thinking I don t see the big advantage to Stage Programming in fact the stage program is longer than the plain RLL program Well now is the time to exercise a bit of faith As control problems grow in complexity stage programming quickly out performs RLL in simplicity program size etc For example consider the diagram below Notice how easy it is to co
16. the motor to raise the door e We transition to the UP state when the up limit switch X1 energizes and turns off the motor e Then nothing happens until another XO press release cycle occurs That takes us to the LOWER state turning on output Y2 to command the motor to lower the door We transition back to the DOWN state when the down limit switch X2 energizes Powerup l S6 DOWN State xo s1 sG Push UP State XO xo 2 JMP Output equations Y1 Raise Y2 Lower SG RAISE State The equivalent stage program is shown to the right For now we 22 will assume the door is down at powerup so the desired powerup SP1 Y1 state is DOWN We make SO an initial stage ISG Stage SO oun remains active until the door control pushbutton activates Then xl a we transition JMP to Push UP stage S1 MP SG A push release cycle of the pushbutton takes us through stage S1 3 UP State to the RAISE stage S2 We use the always on contact SP1 to xo s4 energize the motor s raise command Y1 When the door reaches H maom the fully raised position the up limit switch X1 activates This takes us to the UP Stage S3 where we wait until another door SS Push DOWN State control command occurs xo s5 In the UP Stage S3 a push release cycle of the pushbutton will L CMe take us to the LOWER Stage S5 where we activate Y2 to Sa LOWER SG command the motor to lower the door
17. write the stage program in Step 4 However the program virtually writes itself because of the preparation beforehand Soon you will be able to start with a word description of an application and create a stage program in one easy session DL205 User Manual 4th Edition Rev B 7 9 Chapter 7 RLL Stage Programming Stage Program Example A Garage Door Opener Garage Door Opener Example In this next stage programming example we will create a garage door opener controller Hopefully most readers are familiar with this application and we can have fun besides The first step we must take is to describe how the door opener works We will start by achieving the basic operation waiting to add extra features later stage programs are very easy to modify Our garage door controller has a motor which raises or lowers the door on command The garage owner pushes and releases a momentary pushbutton once to raise the door After the door is up another push 7 release cycle will lower the door In order to identify the inputs and outputs of the ee ca r5 Up limit switch system it s sometimes helpful to sketch its main r4 components as shown in the door side view to the m right The door has an up limit and a down limit Motor Raise switch Each limit switch closes only when the door Lower has reached the end of travel in the corresponding direction In the middle of travel neither limit switch
18. 2 and S4 are Convergence Stages Process A gt Convergence Stage Convergence Stages CV While the converging principle is simple enough it brings a new complication As parallel processing completes the multiple processes almost never finish at the same time In other words how can we know whether Stage S2 or S4 will finish last This is an important point 230 V 240 V 250 1 V 260 because we have to decide how to transition to Stage S5 The solution is to coordinate the transition condition out of convergence stages We accomplish this with a stage type designed for this purpose the Convergence Stage type CV In the example to the right convergence stages S2 and S4 are required to be grouped together as shown No logic is permitted between CV stages The transition condition X3 in this case must be located in the last convergence stage The transition condition only has power flow when all convergence stages in the group are active SEDGE cv Convergence S2 Fa Stages CV S4 X3 S5 H ewn SG S5 DL205 User Manual 4th Edition Rev B 7 19 Chapter 7 RLL Stage Programming Convergence Jump CVJMP 230 V 240 V 250 1 V 260 Convergence Stage Guidelines The following summarizes the requirements in the use of convergence stages including some tips for their effective application Recall the last convergence stage only has p
19. RLL STAGE PROGRAMMING In This Chapter Introduction to Stage Programming 2 eee eee 7 2 Learning to Draw State Transition Diagrams 7 3 Using the Stage Jump Instruction for State Transitions 7 7 Stage Program Example Toggle On Off Lamp Controller 7 8 Four Steps to Writing a Stage Program 0085 7 9 Stage Program Example A Garage Door Opener 7 10 Stage Program Design Considerations 045 7 15 Parallel Processing Concepts oh cianendoee eee eed ohncne ees 7 19 Managing Large Programs 0 lt 6 6 lt nes ee ee seeee seve ees 7 21 RLLPLUS Stage Instructions 45 4 ney eee eed edd aleewedt aa ees 7 23 Questions and Answers about Stage Programming 7 29 Chapter 7 RLL Stage Programming RS Introduction to Stage Programming V 230 Stage Programming available in all DL205 CPUs provides a way to organize and program V 240 complex applications with relative ease when compared to purely relay ladder logic RLL V 250 1 solutions Stage programming does not replace or negate the use of traditional boolean ladder Z 260 programming This is why Stage Programming is also called RLL You will not have to discard any training or experience you already have Stage programming simply allows you to divide and organize a RLL program into groups of ladder instructions called stages This allows quicker and more intuitiv
20. SG V 240 when the CPU enters the run mode allowing for a starting _ S aaa point in the program Initial Stages are also activated by V 250 1 transitional logic a jump or a set stage executed from an V 260 active stage Initial Stages are deactivated one scan after transitional logic a jump or a reset stage instruction is executed Multiple Initial Stages are allowed in a program Operand Data Type DL230 Range DL240 Range DL250 1 Range DL260 Range aaa aaa aaa aaa Stage S 0 377 0 777 0 1777 0 1777 power down and will NOT turn itself on during the first scan E Si ox The Jump instruction allows the program to transition from Mi 230 an active stage which contains the jump instruction to NOTE If the ISG is within the retentive range for stages the ISG will remain in the state it was in before S aaa V 240 another stage which is specified in the instruction The jump I 250 1 will occur when the input logic is true The active stage that JMP contains the Jump will be deactivated 1 scan after the Jump Mi 260 instruction is executed Operand Data Type DL230 Range DL240 Range DL250 1 Range DL260 Range aaa aaa aaa aaa Stage S 0 377 0 777 0 1777 0 1777 Not Jump NJMP The Not Jump instruction allows the program to transition M 230 from an active stage which contains the jump instruction to i 249 another which is specified in the instruction The jump will occu
21. Y3 OUT 20 CVJMP S0 c me Handheld Programmer Keystrokes ISG gt S SG 0 ENT STR gt X IN 0 ENT OUT gt youn 0 ENT STR gt xan 1 ENT JMP gt ssc 1 ENT me _ gt _ sie 1 0 ENT SG gt l sso 1 ENT STR gt xan 2 ENT JMP gt sso 1 1 ENT SHFT c v gt F ssc 1 ENT SHFT c v gt ssc 1 ENT STR gt xan 3 ENT OUT gt yout 3 ENT STR gt xm 4 ENT SHFT c v sHFT ump ssc 0 ENT SG gt sss 2 0 ENT STR SJL 5 ENT JMP gt ssc 0 ENT Chapter 7 RLL Stage Programming Block Call BCALL 230 v 240 V 250 1 V 260 The stage block instructions are used to activate a block of C aaa stages The Block Call Block and Block End instructions BCALL must be used together The BCALL instruction is used to activate a stage block There are several things you need to know about the BCALL instruction e Uses CR Numbers The BCALL appears as an output coil but does not actually refer to a Stage number as you might think Instead the block is identified with a Control Relay Caaa This control relay cannot be used as an output anywhere else in the program e Must Remain Active The BCALL instru
22. age programming state transition diagrams The Need for State Diagrams Sometimes we need to forget about the scan nature of PLCs and focus our thinking toward the states of the process we need to identify Clear thinking and concise analysis of an application gives us the best chance at writing efficient bug free programs State diagrams are tools to help us draw a picture of our process You will discover that if we can get the picture right our program will also be right Inputs Outputs A 2 State Process ON yo o o Motor Consider the simple process shown to the right which controls Ladder vo an industrial motor We will use a green momentary SPST OE g Pogam Q pushbutton to turn the motor on and a red one to turn it off The machine operator will press the appropriate pushbutton for Taron gangen Stat a second or so The two states of our process are ON and OFF W xo The next step is to draw a state transition diagram as shown to Al O a the right It shows the two states OFF and ON with two transition lines in between When the event XO is true we Output equation YO On transition from OFF to ON When X1 is true we transition from ON to OFE If you re following along you are very close to grasping the concept and the problem solving power of state transition diagrams The output of our controller is YO which is true any time we are in the ON state In a boolean sense YO ON state DL205 User Ma
23. an one process Remember you can still have the processes communicate with each other to coordinate their overall activity 2 Draw the Block Diagram Inputs represent all the information the process needs for decisions and outputs connect to all devices controlled by the process e Make lists of inputs and outputs for the process e Assign I O point numbers X and Y to physical inputs and outputs 3 Draw the State Transition Diagram The state transition diagram describes the central function of the block diagram reading inputs and generating outputs e Identify and name the states of the process e Identify the event s required for each transition between states e Ensure the process has a way to re start itself or is cyclical e Choose the powerup state for your process e Write the output equations 4 Write the Stage Program Translate the state transition diagram into a stage program e Make each state a stage Remember to number stages in octal Up to 256 total stages are available in the DL230 CPU Up to 512 total stages are available in the DL240 CPU Up to 1024 total stages are available in the DL250 1 and DL260 CPUs e Put transition logic inside the stage which originates each transition the stage each arrow points away from e Use an initial stage ISG for any states that must be active at powerup e Place the outputs or actions in the appropriate stages You will notice that Steps 1 through 3 prepare us to
24. arlier The Block Call instruction may be used in several contexts Obviously the first execution of a BCALL must occur outside a stage block since stage blocks are initially inactive Still the BCALL may occur on an ordinary ladder rung or it may occur within an active stage as shown below Note that either turning off the BCALL or turning off the stage containing the BCALL will deactivate the corresponding stage block You may also control a stage block with a BCALL in another stage block SG so Stage Block BLK co XO co H ean All rungs in stage SG 2s S11 NOTE Stage Block may come before or after the location of the BCALL instruction in the program The BCALL may be used in many ways or contexts so it can be difficult to find the best usage Remember the purpose of stage blocks is to help you organize the application problem by grouping related stages together Remember that initial stages must exist outside stage blocks 7 22 l DL205 User Manual 4th Edition Rev B Chapter 7 RLL Stage Programming RLLPUs Stage Instructions Stage SG V 230 V 240 V 250 1 active stage Stages are deactivated one scan after transitional logic V 260 Operand Data Type DL230 Range a jump or a reset stage instruction is executed DL240 Range The Stage instructions are used to create structured RLL LUS programs Stages are program se
25. ction actually controls all the stages between the BLK and the BEND instructions even after the stages inside the block have started executing The BCALL must remain active or all the stages in the block will automatically be turned off feither the BCALL instruction or the stage that contains the BCALL instruction goes off then the stages in the defined block will be turned off automatically e Activates First Block Stage When the BCALL is executed it automatically activates the first stage following the BLK instructions Operand Data Type DL240 Range DL250 1 Range DL260 Range aaa aaa aaa Control Relay C 0 777 0 1777 0 3777 Block BLK The Block instruction is a label which marks the beginning BLK 230 V 240 V 250 1 V 260 of a block of stages that can be activated as a group A Stage C aaa instruction must immediately follow the Start Block instruction Initial Stage instructions are not allowed in a block The control relay Caaa specified in Block instruction must not be used as an output anywhere else in the program Block End BEND 230 V 240 V 250 1 V 260 The Block End instruction is a label used with the Block instruction It marks the end of a block of stages There is no BEND operand with this instruction Only one Block End is allowed per Block Call Operand Data Type DL240 Range DL250 1 Range DL260 Range aaa aaa aaa Control Relay C 0 777 0 1777 0 3777
26. e Stage JMP instruction its only advantage However it is not as easy to make program changes as using the Stage JMP Therefore we advise using Stage JMP transitions for most programs 7 18 DL205 User Manual 4th Edition Rev B i ZASA Chapter 7 RLL Stage Programming Parallel Processing Concepts Parallel Processes Previously in this chapter we discussed how a state may transition to either one state or another called an exclusive transition In other cases we may need to branch simultaneously to two or more parallel processes as shown below It is acceptable to use all JMP instructions as shown or we could use one JMP and a Set Stage bit instruction s at least one must be a JMP in order to leave 1 Remember that all instructions in a stage execute even when it transitions the JMP is nota GOTO Process A aT Push On State X0 S2 H ro S4 Process B vP Note that if we want Stages S2 and S4 to energize exactly on the same scan both stages must be located below Stage S1 in the ladder program see the explanation at the bottom of page 7 7 Overall parallel branching is easy Converging Processes Now we consider the opposite case of parallel branching which is converging processes This simply means we stop doing multiple things and continue doing one thing at a time In the figure below processes A and B converge when stages S2 and S4 transition to S5 at some point in time So S
27. e Stages CV When all of the Converge Stages within a group become S aaa active the CVJMP instruction and any additional logic in the final CV stage will be executed All preceding CV stages must be active before the final CV stage logic can be executed All Converge Stages are deactivated one scan after the CVJMP instruction is executed Additional logic instructions are only allowed following the S aaa last Converge Stage instruction and before the CVJMP cVJMP instruction Multiple CVJUMP instructions are allowed Converge Stages must be programmed in the main body of the application program This means they cannot be programmed in Subroutines or Interrupt Routines Operand Data Type DL240 Range DL250 1 Range DL260 Range aaa aaa aaa Stage S 0 777 0 1777 0 1777 DL205 User Manual 4th Edition Rev B 7 25 Chapter 7 RLL Stage Programming a In the following example when Converge Stages S10 and S11 are both active the CVJMP instruction will be executed when X4 is on The CVJMP will deactivate 10 and S11 and activate 20 Then if X5 is on the program execution will jump back to the initial stage S0 DirectSOFT ISG SO X0 X1 SG S1 X2 Yo OUT s1 JMP 10 JMP S11 i k me CV S10 CV 11 X3 X4 SG S20 7 26 DL205 User Manual 4th Edition Rev B X5
28. e ladder program development than traditional RLL alone provides d 49 z 39 Overcoming Stage Fright 7 Many PLC programmers in the industry have RST become comfortable using RLL for every PLC program they write but often remain skeptical Xx C1 Yo or even fearful of learning new techniques such SET as stage ne While RLL is great at Is 7 solving boolean logic relationships it has stacer disadvantages as well i e Large programs can become almost unmanageable because of a lack of structure ii Bide ouT e In RLL latches must be tediously created from self latching relays e When a process gets stuck it is difficult to find the rung where the error occurred e Programs become difficult to modify later because they do not intuitively resemble the application problem they are solving It s easy to see that these inefficiencies consume a lot of additional time and time is money Stage programming overcomes these obstacles We believe a few moments of studying the stage concept is one of the greatest investments in programming speed and efficiency a PLC programmer can make So we encourage you to study stage programming and add it to your toolbox of programming techniques This chapter is designed as a self paced tutorial on stage programming For best results e Start at the beginning and do not skip over any sections e Study each stage programing conc
29. ecause it is not the primary path a ch Inputs Outputs Toggle xo Y1 Down limit Raise eee Lower LYS Light We can think of the Light state as a parallel process to the raise and lower state The paths to the Light state are not a transition Stage JMP but a State Set command In the logic of the Light stage we will place a three minute timer When it expires timer bit TO turns on and resets the Light stage The path out of the Light stage goes nowhere indicating the Light stage becomes inactive and the light goes out Push UP Output equations Xo 7 12 DL205 User Manual 4th Edition Rev B XO Y1 RAISE Y2 LOWER Y3 LIGHT Chapter 7 RLL Stage Programming Using a Timer Inside a Stage The finished modified program is shown to the right The shaded areas indicate the program additions In the Push UP stage S1 we add the Set Stage Bit S6 instruction When contact XO opens we transition from S1 and go to two new active states S2 and S6 In the Push DOWN state S4 we make the same additions So any time someone presses the door control pushbutton the light turns on Most new stage programmers would be concerned about where to place the Light Stage in the ladder and how to number it The good news is that it doesn t matter e Choose an unused Stage number and use it for the new stage and as the reference from other s
30. ept by working through each example The examples build progressively on each other e Read the Stage Questions and Answers at the end of the chapter for a quick review 7 2 DL205 User Manual 4th Edition Rev B Chapter 7 RLL Stage Programming Learning to Draw State Transition Diagrams Ladder Introduction to Process States Inputs Program Those familiar with ladder program execution know the CPU must scan the ladder program repeatedly over and over Its three basic steps are 1 Read the inputs PLC Scan 1 Read Execute Write 2 Read Execute Write Outputs 2 Execute the ladder program 3 Write the outputs The benefit is that a change at the inputs can affect the 9 PLE Etves outputs in just a few milliseconds Most manufacturing processes consist of a series of activities or conditions each lasting for several seconds minutes or even hours We might call these process states which are either active or inactive at any particular time A challenge for RLL programs is that a particular input event may last for a brief instant We typically create latching relays in RLL to preserve the input event in order to maintain a process state for the required duration We can organize and divide ladder logic into sections called stages representing process states But before we describe stages in detail we will reveal the secret to understanding st
31. for stages the ISG will remain in the state it was in before power down and will NOT turn itself on during the first scan DL205 User Manual 4th Edition Rev B 7 5 Chapter 7 RLL Stage Programming We can mark our desired powerup state as shown to Powerup xo the right which helps us remember to use the appropriate Initial Stages when creating a stage program It is permissible to have as many initial Corr CON stages as the process requires XI What Stage Bits Do You may recall that a stage is a section of ladder program which is either active or inactive at a given moment All stage bits S0 to Sxxx reside in the PLC s image register as individual status bits Each stage bit is either a boolean 0 or 1 at any time Program execution always reads ladder rungs from top to bottom and from left to right The drawing below shows the effect of stage bit status The ladder rungs below the stage instruction continuing until the next stage instruction or the end of program belong to stage 0 Its equivalent operation is shown on the right When S0 is true the two rungs have power flow e If Stage bit SO 0 its ladder rungs are not scanned executed e If Stage bit SO 1 its ladder rungs are scanned executed Actual Program Appearance Functionally Equivalent Ladder SG so 92 C C gt includes all rungs i
32. gments which can be activated by transitional logic a jump or a set stage that is executed from an SG S aaa DL250 1 Range DL260 Range aaa aaa aaa aaa Stage 0 377 0 777 0 1777 0 1777 The following example is a simple RLL 4YS program This program utilizes the initial stage stage and jump instruction to create a structured program DirectSOFT Handheld Programmer Keystrokes ISG gt SG 0 ENT ISG SO STR gt X IN 0 ENT OUT gt your 1 0 ENT STR gt X IN 1 ENT X0 Y10 SET gt S SG 2 ENT OUT STR gt X IN 5 ENT x1 2 JMP gt see 1 ENT SET SG gt S SG 1 ENT x5 S1 STR gt X IN 2 ENT JMP OUT gt yout 1 1 ENT SG gt S SG 2 ENT SG S1 STR gt X IN 6 ENT OUT 5 J voun 1 2 ENT STR gt X IN 7 ENT X2 a AND gt ssc 1 ENT JMP gt ssc 0 ENT SG S2 X6 Y12 ouT X7 S1 so WP DL205 User Manual 4th Edition Rev B 7 23 Chapter 7 RLL Stage Programming Initial Stage ISG The Initial Stage instruction is normally used as the first M 230 segment of an RLL LUS program Initial stages will be active I
33. itely Stage Counter The counter in the above example is a special Stage Counter Note that it does not have a reset input The count is reset by executing a Reset instruction naming the counter bit CTO in this case The Stage Counter has the benefit that its count may be globally reset from other stages The standard Counter instruction does not have this global reset capability You may still use a regular Counter instruction inside a stage however the reset input to the counter is the only way to reset it Hmo SG S1 Push On State X0 S2 io So ON State SP1 YO ou x0 S3 Cup mes Push Off State x0 so A uP ee Supervisor State S1 H SGCNT CTO K5000 DL205 User Manual 4th Edition Rev B 7 17 Chapter 7 RLL Stage Programming a RRR Unconditional Outputs a As in most example programs in this chapter SG and Stage 0 to the right your application So may require a particular output to be ON SP1 Yo unconditionally when a particular stage is out active Until now the examples always use the SP1 special relay contact always on in SG Unconditional series with the output coils It s possible to S1 Output omit the contact as long as you place any ae unconditional outputs first at the top of a oun stage section of ladder The first rung of i Pas Stage 1 doe
34. n On the following scan that stage is not executed because it 1s inactive e The Stage named in the Stage JMP instruction will be executed upon its next occurrence If located past under the current stage it will be executed on the same scan If located before above the current stage it will be executed on the following scan Q How can I know when to use stage JMP versus a Set Stage Bit or Reset Stage Bit A These instructions are used according to the state diagram topology you have derived e Use a Stage JMP instruction for a state transition moving from one state to another e Use a Set Stage Bit instruction when the current state is spawning a new parallel state or stage sequence or when a supervisory state is starting a state sequence under its command e Use a Reset Bit instruction when the current state is the last state in a sequence and its task is complete or when a supervisory state is ending a state sequence under its command Q What is an initial stage and when do I use it A An initial stage ISG is automatically active at powerup Afterwards it works just like any other stage You can have multiple initial stages if required Use an initial stage for ladder that must always be active or as a starting point Q Can I have place program ladder rungs outside of the stages so they are always on A It is possible but it s not good software design practice Place ladder that must always be active in an ini
35. n stage L Stage Instruction Characteristics So The inline stage boxes on the left power rail divide the ladder gt program rungs into stages Some stage rules are e Execution Only logic in active stages are executed on any i scan SG 1 e Transitions Stage transition instructions take effect on the next occurrence of the stages involved 2 e Octal numbering Stages are numbered in octal like I O D points etc So S8 is not valid aa e Total Stages The maximum number of stages is CPU S2 dependent c gt e No duplicates Each stage number is unique and can be used gt just once J e Any order You can skip numbers and sequence the stage END numbers in any order e Last Stage The last stage in the ladder program includes all rungs from its stage box until the end coil 7 6 DL205 User Manual 4th Edition Rev B Chapter 7 RLL Stage Programming a Using the Stage Jump Instruction for State Transitions Stage Jump Set and Reset Instructions The Stage JMP instruction we have used deactivates the stage in which the instruction occurs while activating the stage in the JMP instruction Refer to the state transition shown below When contact X0 energizes the state transition from SO to S1 occurs The two stage examples shown below are equivalent So the Stage Jump instruction is equal to a Stage Reset of the current stage plus a Stage Set instruction for the stage to which we want to tran
36. nual 4th Edition Rev B 7 3 Chapter 7 RLL Stage Programming The state transition diagram to the right is a picture XO of the solution we need to create The beauty of it is this it expresses the problem independently of the programming language we may use to realize it In x1 other words by drawing the diagram we have already solved the control problem Output equation YOS ON First we ll translate the state diagram to traditional RLL Then we ll show how easy it is to translate the diagram into a stage programming solution RLL Equivalent Set Reset Output The RLL solution is shown to the right It consists of xo x1 Yo a self latching motor output coil YO When the On VA oud pushbutton X0 is pressed output coil YO turns on and the YO contact on the second row latches itself on So XO sets the latch YO on and it remains on Latch after the XO contact opens w When the Off pushbutton X1 is pressed it opens the normally closed X1 contact which resets the latch Motor output YO turns off Stage Equivalent The stage program solution is shown to the right SG The two inline stage boxes SO and S1 correspond to so OFF State the two states OFF and ON The ladder rung s Tiahidition below each stage box belong to each respective stage x a4 This means that the PLC only has to scan those rungs Lt Gp when the corresponding stage is active For
37. ocess GD ise Powerup Initialization E Stop and Alarm Monitoring Operator Interface 7 Ca G In a typical application the separate stage sequences above operate as follows e Powerup Initialization This stage contains ladder rung tasks performed once at powerup Its last rung resets the stage so this stage is only active for one scan or only as many scans that are required e Main Process This stage sequence controls the heart of the process or machine One pass through the sequence represents one part cycle of the machine or one batch in the process e E Stop and Alarm Monitoring This stage is always active because it is watching for errors that could indicate an alarm condition or require an emergency stop It is common for this stage to reset stages in the main process or elsewhere in order to initialize them after an error condition e Operator Interface This is another task that must always be active and ready to respond to an operator It allows an operator interface to change modes etc independently of the current main process step Although we have separate processes there can be Operator interes coordination among them For example in an error condition the Status Stage may want to Control automatically switch the operator interface to the status mode to show error information as shown to the right The monitor stage could set the stage bit Monitor C Status for Status and
38. om the numbering of the blocks DL205 User Manual 4th Edition Rev B 7 21 Chapter 7 RLL Stage Programming Block Call BCALL 230 v 240 V 250 1 V 260 The purpose of the Block Call instruction is to activate a stage block At powerup or upon Program to Run mode transitions all stage blocks and the stages within them are inactive Shown in the figure below the Block Call instruction is a type of output coil When the XO contact is closed the BCALL will cause the stage block referenced in the instruction C0 to become active When the BCALL is turned off the corresponding stage block and the stages within it become inactive We must avoid confusing block call operation with how a subroutine call works After a BCALL coil executes program execution continues with the next program rung Whenever program execution arrives at the ladder location of the stage block named in the BCALL then logic within the block executes because the block is now active Similarly do not classify the BCALL as type of state transition is not a JMP Block CO x0 co H CBCALL Activate s next rung CO When a stage block becomes active the first stage in the block automatically becomes active on the same scan The first stage in a block is the one located immediately under the block BLK instruction in the ladder program So that stage plays a similar role to the initial type stage we discussed e
39. ower flow cv when all CV stages in the group are active To 2 Convergence complement the convergence stage we need a new Jump jump instruction The Convergence Jump CVJMP cv shown to the right will transition to Stage S5 when S4 X3 is active as one might expect but it also as be automatically resets all convergence stages in the group Ly CCVM This makes the CVJMP jump a very powerful instruction Note that this instruction may only be SG used with convergence stages S5 e A convergence stage is to be used as the last stage of a process which is running in parallel to another process or processes A transition to the convergence stage means that a particular process is through and represents a waiting point until all other parallel processes also finish e The maximum number of convergence stages which make up one group is 17 In other words a maximum of 17 stages can converge into one stage e Convergence stages of the same group must be placed together in the program connected on the power rail without any other logic in between e Within a convergence group the stages may occur in any order top to bottom It does not matter which stage is last in the group because all convergence stages have to be active before the last stage has power flow e The last convergence stage of a group may have ladder logic within the stage However this logic will not execute until all convergence stages of the group are active
40. r when the input logic is off The active stage that NJMP Vv 250 1 contains the Not Jump will be deactivated 1 scan after the Mi 260 Not Jump instruction is executed Operand Data Type DL230 Range DL240 Range DL250 1 Range DL260 Range aaa aaa aaa aaa Stage S 0 377 0 777 0 1777 0 1777 7 24 DL205 User Manual 4th Edition Rev B Chapter 7 RLL Stage Programming eT In the following example when the CPU begins program execution only ISG 0 will be active When X1 is on the program execution will jump from Initial Stage 0 to Stage 1 In Stage 1 if X2 is on output Y5 will be turned on If X7 is on program execution will jump from Stage 1 to Stage 2 If X7 is off program execution will jump from Stage 1 to Stage 3 DirectSOFT Handheld Programmer Keystrokes ISG gt ssc 0 ENT ENT ISG 50 STR gt X IN 1 JMP gt sso 1 ENT yi s1 SG gt S SG 1 ENT JMP STR STP xin 2 ENT OUT gt yout 5 ENT SG S1 STR gt X IN 7 ENT JMP gt S SG 2 ENT x2 YS SHFT N JMP gt OUT S SG 3 ENT x7 S2 JMP s3 NJMP Converge Stage CV and Converge Jump CVJMP 230 V 240 V 250 1 V 260 The Converge Stage instruction is used to group certain stages together by defining them as Converg
41. rocess i i i nputs Outputs In the process shown to the right we use an ordinary i momentary pushbutton to control a light bulb The vane 5 3 Toggle ladder program will latch the switch input so that we _o o X0 Ladder yo will push and release to turn on the light push and Program release again to turn it off sometimes called toggle function Sure we could buy a mechanical switch with the alternate on off action built in However this example is educational and also fun X0 Next we draw the state transition diagram A typical first Corr X D approach is to use XO for both transitions like the example shown to the right However this is incorrect Output equation YO ON please keep reading Powerup Note that this example differs from the motor example because now we have only one pushbutton When we press the pushbutton both transition conditions are met We would transition around the state diagram at top speed If implemented in Stage this solution would flash the light on or off each scan obviously undesirable The solution is to make the push and the release of the pushbutton separate events Refer to the new state transition diagram below At powerup we enter the OFF state When switch X0 is pressed we enter the Press ON state When it is released we enter the ON state Note that X0 with the bar above it denotes XO NOT
42. rrelate the OFF and ON states of the state SG 3 S0 OFF State transition diagram below to the stage program at the right Now we challenge anyone to E at 5 easily identify the same states in the RLL proper on the SG ON State previous page Initial Stages Xo Fi our At powerup and Program to 7 so Run Mode transitions the Corr i CON ume PLC always begins with all normal stages SG off So the stage programs shown so far L Powerup in OFF State have actually had no way to get started because rungs are ISG k not scanned unless their stage is active InitialStage Assume that we want to always begin in the Off state xo Sl motor off which is how the RLL program works The H v Initial Stage ISG is defined to be active at powerup In 3G the modified program to the right we have changed stage S1 SO to the ISG type This ensures the PLC will scan SP1 yo contact XO after powerup because Stage SO is active Our After powerup an Initial Stage ISG works just like any X1 SO other stage JMB We can change both programs so that the motor is ON at powerup In the RLL below we must add a first scan relay Powerup in ON State SPO latching YO on In the stage example to the right we simply make Stage S1 an initial stage ISG instead of S0 S0 x0 s1 H mo Powerup in ON State x0 x1 Yo Se 4 Initial Stage V4 Cud SP1 Yo x0 First Scan Ou x1 so SPO aS NOTE If the ISG is within the retentive range
43. s this ouT WARNING Unconditional outputs placed SG elsewhere in a stage do not necessarily remain S2 on when the stage is active In Stage 2 to the xo yi right YO is shown as an unconditional output E OUT but its powerflow comes from the rung above So YO status will be the same as Y1 is not PG correct OUT Power Flow Transition Technique Our discussion of state transitions has shown how the Stage JMP instruction makes the current stage inactive and the next stage named in the JMP active As an alternative way to enter this in DirectSOFT you may use the power flow method for stage transitions The main requirement is the current stage be located directly above the next jump to stage in the ladder program This arrangement is shown in the diagram below by stages SO and S1 respectively Coo 2 C st SG SG so so xo S1 All other rungs in stage H o 5 Equivalent SG 1 I Power flow S1 transition SG S1 Recall the Stage JMP instruction may occur anywhere in the current stage and the result is the same However power flow transitions shown above must occur as the last rung in a stage All other rungs in the stage will precede it The power flow transition method is also achievable on the handheld programmer by simply following the transition condition with the Stage instruction for the next stage The power flow transition method does eliminate on
44. sition X0 SG SG S0 S0 s1 Equivalent xo so e X0 H co H eD c Please Read Carefully The jump instruction is easily misunderstood The jump does not occur immediately like a GOTO or GOSUB program control instruction when executed Here s how it works e The jump instruction resets the stage bit of the stage in which it occurs All rungs in the stage still finish executing during the current scan even if there are other rungs in the stage below the jump instruction e The reset will be in effect on the following scan so the stage that executed the jump instruction previously will be inactive and bypassed e The stage bit of the stage named in the Jump instruction will be set immediately so the stage will be executed on its next occurrence In the left program shown below stage S1 executes during the same scan as the JMP S1 occurs in SO In the example on the right Stage S1 executes on the next scan after the JMP S1 executes because stage S1 is located above stage S0 SG SG Executes on next so S1 scan after Jmp X0 S1 S1 Yo pt ne 4 o SG Executes on same SG S1 scan as Jmp so S1 YO XO a LY o H Ha NOTE Assume we start with Stage 0 active and Stage 1 inactive for both examples DL205 User Manual 4th Edition Rev B 7 7 Chapter 7 RLL Stage Programming Stage Program Example Toggle On Off Lamp Controller A 4 State P
45. tages e Placement in the program is not critical so we place it at the end You might think that each stage has to be directly under the stage that transitions to it While it is good practice it is not required that s good because our two locations for the Set S6 instruction make that impossible Stage numbers and how they are used determines the transition paths In stage S6 we turn on the safety light by energizing Y3 Special relay contact SP1 is always on Timer TO times at 0 1 second per count To achieve 3 minutes time period we calculate K 3 min x 60 sec min 0 1 sec count K 1800 counts The timer has power flow whenever stage S6 is active The corresponding timer bit TO is set when the timer expires So three minutes later TO 1 and the instruction Reset S6 causes the stage to be inactive While Stage S6 is active and the light is on stage transitions in the primary path continue normally and independently of Stage 6 That is the door can go up down or whatever but the light will be on for precisely 3 minutes ISG I So DOWN State X0 s1 a uP ae Push UP State x0 s2 M mp s6 A L SET S2 RAISE State SP1 Y1 OuT x1 3 mp SG 3 UP State x0 S4 1 ump a Push DOWN State x0 s5 4 mp S6 SET SG D S5 LOWER State SP1 Y2 OuT
46. tial stage and do not reset that stage or use a Stage JMP instruction inside it It can start other stage sequences at the proper time by setting the appropriate Stage Bit s Q Can I have more than one active stage at a time A Yes and this is a normal occurrence for many programs However it is important to organize your application into separate processes each made up of stages And a good process design will be mostly sequential with only one stage on at a time However all the processes in the program may be active simultaneously 7 30 DL205 User Manual 4th Edition Rev B
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