Download - Step 7 Fundamentals Handbook
The Case of the Missing SIMATIC Step 7 Documentation
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The Case of the Missing SIMATIC Step 7Documentation“We had documentation at one time.”
Sound familiar? Have you suddenly found changes that have been made in the PLC but not inthe offline program? Nobody knows what happened.
Unfortunately this is an all too common phenomena with the Siemens SIMATIC Step 7software. The problems stem from the flexibility of the software both for downloading andediting the online program. If the person is not familiar with the software it’s very easy to getconfused if the changes are being made on the computer or in the controller.
How to solve this problem? Let’s first of all review some basic terminology. After that is a stepby step best practice when editing programs. Finally, we’ll highlight the pitfalls and theindicators that tell you whether you are offline or online. This procedure applies to SIMATICStep 7 version 5.4.
Terminology
Offline program – The program that is stored on the hard disk of the computer. This willcontain the documentation. It’s very important to keep a pristine copy of the offline programas the associated documentation is not stored in the PLC.
Online program – This is the program resident in the PLC.
Download – The act of taking the offline program on the computer and downloading it intothe PLC.
Upload – Taking the program in the PLC and bringing it up to the computer. Doing thiswithout having the associated offline program open will cause a loss of documentation.
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Save – Stores the open block onto the hard drive. It’s important to realize that an edited blockcan be downloaded to the PLC without saving it offline. Note that this only saves the openedblock and not any others that are concurrently open.
These may seem like simple terms but it’s important to understand how they’re used in theSiemens environment.
Here are some other terms that may come up.
PG/PC – This is Siemens way of referring to a PC or laptop running the SIMATIC software.
Nodes – Refers to any programmable device (in our case a PLC) in the network which willhave its own unique address.
Best Practice
The best practice is to make sure you are working from an offline file. There really isn’t anyreason to be working on the program inside the PLC. Of course, this assumes that you have agood working copy to begin with. The “golden” copy of the program should live somewhere ona network server or have a dedicated place on one computer or laptop. I’ve even heard ofsome companies using USB memory sticks to store the latest and greatest which is great but anoriginal copy should still live on a computer that is backed up.
1. Open the offline file from the File pull down menu and select Open or use the Open Project icon on the toolbar. In the dialog box select the projectunder the User Project tab. Click OK. You may have to select Browse to find it in thedirectory structure. Note if the Manager was closed with a project open then it will openback up to that project automatically.
2. Expand the project tree down to the program files and select the Blocksfolder. Good practice dictates that all blocks should be opened from here.
3. Once changes have been made:1. Save the block to the hard disk by clicking the Save icon (or menu item
The Case of the Missing SIMATIC Step 7 Documentation
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File | Save)2. Download the block by clicking the Download icon (or menu item PLC |
Download). If the block all ready exists in the PLC then it will confirm that you wantto overwrite it1. Click Yes.
3. Note that downloading from here only sends that one block to the PLC. It does notdownload the entire program.
4. To monitor the block make sure to open it using steps 1 through 3 and thenpress the Monitor icon (or menu item Debug | Monitor). The window’s title bar willhighlight a lovely shade of blue to indicate a connection to the CPU. It’s important tonote here that you are still working with the program on the computer and not the PLC. If the procedure in step 3 has not been followed then discrepancies can occur betweenwhat you are monitoring in the PLC and what is displayed in the SIMATIC software.
That’s it. Following these simple steps will save a lot of headaches.
The Pitfalls and Warning Signs
So where do some people get lost? Here are some common mistakes and their warning signs. If you get any of these dialog boxes then you should really back out and start over becauseyou’re on the road to losing your documentation.
The Case of the Missing SIMATIC Step 7 Documentation
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These dialog boxes are telling you that it cannot find the documentation for the localparameters and symbols. More then likely it will also not show any network comments or titles.
The result of opening the block looks like this
The Case of the Missing SIMATIC Step 7 Documentation
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This is an example void of documentation. Notice the local parameters all say TEMP. Thereare no comments or titles. There are no symbols so it’s all in direct addressing. The properlydocumented copy looks like this...
Pitfall #1 – Using Accessible Nodes to Open Blocks
The Display Accessible Nodes selection under the PLC menu is a handy way to see what isconnected to the network but it should never be used to open blocks. Opening blocks fromhere uploads it straight from the PLC and produces the warnings dialog boxes shown above.
The Case of the Missing SIMATIC Step 7 Documentation
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Pitfall #2 – Viewing Online from SIMATIC manager
Once a project is open and a connection to a PLC is established then selecting the Onlinebutton (menu View | Online) brings up a similar project tree showing the contents insidethe PLC. The window title bar is highlighted in blue to indicate its online status. Working fromthis window presents less of a danger for losing documentation but it is confusing and couldlead to problems. For instance if a block is renamed offline and then the old one is openedonline then it will have no associated documentation.
The proper way to view a block online is to open the block and select the Establish Connectionto Configured CPU icon . Just make sure what you are viewing has been downloaded to thePLC.
The Case of the Missing SIMATIC Step 7 Documentation
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Pitfall #3 – Opening the Online Partner
If an offline block is open then selecting the Open Offline/Online Partner icon (menu itemFile | Open Online) will switch it to the online version of the block for editing. Essentially thisputs you in the same place as pitfall #2.
Conclusion
Programming with SIMATIC Step 7 is different enough from other types of PLCs to throw offthe casual user. Always working from the offline copy will make it less likely to screw up. Opening up a block from the accessible nodes window is always a no-no. Likewise, opening ablock from a window that has a highlighted blue title bar will also cause potential problems. Besure and read all dialog boxes especially the ones we’ve shown in the article. Avoid the pitfallsand keep that documentation. Mystery solved.
Footnote:
(1) Siemens dialog boxes have an option that says, “Do not display this message again.” This
The Case of the Missing SIMATIC Step 7 Documentation
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is handy for some annoying pop ups but it is really not a good idea to turn off important oneslike warnings for overwriting blocks. These warnings are especially crucial if you are workingon real machinery. If more then one person is using the software then you can reset thesemessages to display again by going to the SIMATIC Manager and select the menu Options |Customize. Click the General tab and press the Activate button. If it’s grayed out then allmessages are set to display.
S7 Library Functions
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S7 Library FunctionsI couldn't find a complete listing of all the function blocks in the standard Siemens S7 Librariesso I made one myself. It helps me get a better overview of what is available. The completelisting is also available as an Excel spreadsheet so you can sort or adjust to your needs.
System Function Blocks
Number Name Family Description
SFB 0 CTU IEC_TC Count Up
SFB 1 CTD IEC_TC Count Down
SFB 2 CTUD IEC_TC Count Up/Down
SFB 3 TP IEC_TC Generate a Pulse
SFB 4 TON IEC_TC Generate an On Delay
SFB 5 TOF IEC_TC Generate an Off Delay
SFB 8 USEND COM_FUNC Uncoordinated Sending of Data
SFB 9 URCV COM_FUNC Uncoordinated Receiving of Data
SFB 12 BSEND COM_FUNC Sending Segmented Data
SFB 13 BRCV COM_FUNC Receiving Segmented Data
SFB 14 GET COM_FUNC Read Data from a Remote CPU
SFB 15 PUT COM_FUNC Write Data to a Remote CPU
SFB 16 PRINT COM_FUNC Send Data to Printer
SFB 19 START COM_FUNC Initiate a Warm or Cold Restart on a Remote Device
SFB 20 STOP COM_FUNC Changing a Remote Device to the STOP State
SFB 21 RESUME COM_FUNC Initiate a Hot Restart on a Remote Device
SFB 22 STATUS COM_FUNC Query the Status of a Remote Partner
SFB 23 USTATUS COM_FUNC Receive the Status of a Remote Device
SFB 29 HS_COUNT COUNTERS Counter (high-speed counter, integrated function) (onlyexist on the CPU 312 IFM and CPU 314 IFM)
SFB 30 FREQ_MES COUNTERS Frequency Meter (frequency meter, integrated function(only exist on the CPU 312 IFM and CPU 314 IFM)
SFB 31 NOTIFY_8P COM_FUNC Generating block related messages withoutacknowledgement indication
SFB 32 DRUM TIMERS Implement a Sequencer
SFB 33 ALARM COM_FUNC Generate Block-Related Messages with AcknowledgmentDisplay
SFB 34 ALARM_8 COM_FUNC Generate Block-Related Messages without Values for 8
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Signals
SFB 35 ALARM_8P COM_FUNC Generate Block-Related Messages with Values for 8Signals
SFB 36 NOTIFY COM_FUNC Generate Block-Related Messages withoutAcknowledgment Display
SFB 37 AR_SEND COM_FUNC Send Archive Data
SFB 38 HSC_A_B COUNTERS Counter A/B (integrated function) (only exist on the CPU314 IFM)
SFB 39 POS ICONT Position (integrated function) (only exist on the CPU 314IFM)
SFB 41 CONT_C ICONT Continuous Control (only exist on the CPU 314 IFM)
SFB 42 CONT_S ICONT Step Control (only exist on the CPU 314 IFM)
SFB 43 PULSEGEN ICONT Pulse Generation (only exist on the CPU 314 IFM)
SFB 44 ANALOG TEC_FUNC Positioning with Analog Output (only exist on the S7-300C CPUs)
SFB 46 DIGITAL TEC_FUNC Positioning with Digital Output (only exist on the S7-300CCPUs)
SFB 47 COUNT TEC_FUNC Controlling the Counter (only exist on the S7-300C CPUs)
SFB 48 FREQUENC TEC_FUNC Controlling the Frequency Measurement (only exist onthe S7-300C CPUs)
SFB 49 PULSE TEC_FUNC Controlling Pulse Width Modulation (only exist on the S7-300C CPUs)
SFB 52 RDREC DP Reading a Data Record
SFB 53 WRREC DP Writing a Data Record
SFB 54 RALRM DP Receiving an Interrupt
SFB 60 SEND_PTP TEC_FUNC Sending Data (ASCII, 3964(R)) (only exist on the S7-300C CPUs)
SFB 61 RECV_PTP TEC_FUNC Receiving Data (ASCII, 3964(R)) (only exist on the S7-300C CPUs)
SFB 62 RES_RECV TEC_FUNC Deleting the Receive Buffer (ASCII, 3964(R)) (only existon the S7-300C CPUs)
SFB 63 SEND_RK TEC_FUNC Sending Data (RK 512) (only exist on the S7-300C CPUs)
SFB 64 FETCH_RK TEC_FUNC Fetching Data (RK 512) (only exist on the S7-300C CPUs)
SFB 65 SERVE_RK TEC_FUNC Receiving and Providing Data (RK 512) (only exist on theS7-300C CPUs)
SFB 75 SALRM DP Send interrupt to DP master
SFB 81 RD_DPAR IO_FUNCT Read Predefined Parameter
System Function Calls
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Number Name Family Description
SFC 0 SET_CLK CLK_FUNC Set System Clock
SFC 1 READ_CLK CLK_FUNC Read System Clock
SFC 2 SET_RTM CLK_FUNC Set Run-time Meter
SFC 3 CTRL_RTM CLK_FUNC Start/Stop Run-time Meter
SFC 4 READ_RTM CLK_FUNC Read Run-time Meter
SFC 5 GADR_LGC IO_FUNCT Query Logical Address of a Channel
SFC 6 RD_SINFO DB_FUNCT Read OB Start Information
SFC 7 DP_PRAL DP Trigger a Hardware Interrupt on the DP Master
SFC 9 EN_MSG COM_FUNC Enable Block-Related, Symbol-Related and Group StatusMessages
SFC 10 DIS_MSG COM_FUNC Disable Block-Related, Symbol-Related and Group StatusMessages
SFC 11 DPSYC_FR DP Synchronize Groups of DP Slaves
SFC 12 D_ACT_DP DP Deactivation and activation of DP slaves
SFC 13 DPNRM_DG DIAGNSTC Read Diagnostic Data of a DP Slave (Slave Diagnostics)
SFC 14 DPRD_DAT DP Read Consistent Data of a Standard DP Slave
SFC 15 DPWR_DAT DP Write Consistent Data to a DP Standard Slave
SFC 17 ALARM_SQ PMC_FUNC Generate Acknowledgeable Block-Related Messages
SFC 18 ALARM_S PMC_FUNC Generate Permanently Acknowledged Block-RelatedMessages
SFC 19 ALARM_SC PMC_FUNC Query the Acknowledgment Status of the last ALARM_SQEntering State Message
SFC 20 BLKMOV MOVE Copy Variables
SFC 21 FILL MOVE Initialize a Memory Area
SFC 22 CREAT_DB DB_FUNCT Create Data Block
SFC 23 DEL_DB DB_FUNCT Delete Data Block
SFC 24 TEST_DB DB_FUNCT Test Data Block
SFC 25 COMPRESS DB_FUNCT Compress the User Memory
SFC 26 UPDAT_PI IO_FUNCT Update the Process Image Update Table
SFC 27 UPDAT_PO IO_FUNCT Update the Process Image Output Table
SFC 28 SET_TINT PGM_CNTL Set Time-of-Day Interrupt
SFC 29 CAN_TINT PGM_CNTL Cancel Time-of-Day Interrupt
SFC 30 ACT_TINT PGM_CNTL Activate Time-of-Day Interrupt
SFC 31 QRY_TINT PGM_CNTL Query Time-of-Day Interrupt
SFC 32 SRT_DINT PGM_CNTL Start Time-Delay Interrupt
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SFC 33 CAN_DINT PGM_CNTL Cancel Time-Delay Interrupt
SFC 34 QRY_DINT PGM_CNTL Query Time-Delay Interrupt
SFC 35 MP_ALM PGM_CNTL Trigger Multicomputing Interrupt
SFC 36 MSK_FLT DIAGNSTC Mask Synchronous Errors
SFC 37 DMSK_FLT DIAGNSTC Unmask Synchronous Errors
SFC 38 READ_ERR DIAGNSTC Read Error Register
SFC 39 DIS_IRT IRT_FUNC Disable New Interrupts and Asynchronous Errors
SFC 40 EN_IRT IRT_FUNC Enable New Interrupts and Asynchronous Errors
SFC 41 DIS_AIRT IRT_FUNC Delay Higher Priority Interrupts and Asynchronous Errors
SFC 42 EN_AIRT IRT_FUNC Enable Higher Priority Interrupts and AsynchronousErrors
SFC 43 RE_TRIGR PGM_CNTL Re-trigger Cycle Time Monitoring
SFC 44 REPL_VAL DIAGNSTC Transfer Substitute Value to Accumulator 1
SFC 46 STP PGM_CNTL Change the CPU to STOP
SFC 47 WAIT PGM_CNTL Delay Execution of the User Program
SFC 48 SNC_RTCB CLK_FUNC Synchronize Slave Clocks
SFC 49 LGC_GADR IO_FUNCT Query the Module Slot Belonging to a Logical Address
SFC 50 RD_LGADR IO_FUNCT Query all Logical Addresses of a Module
SFC 51 RDSYSST DIAGNSTC Read a System Status List or Partial List
SFC 52 WR_USMSG DIAGNSTC Write a User-Defined Diagnostic Event to the DiagnosticBuffer
SFC 54 RD_PARM IO_FUNCT Read Defined Parameters
SFC 55 WR_PARM IO_FUNCT Write Dynamic Parameters
SFC 56 WR_DPARM IO_FUNCT Write Default Parameters
SFC 57 PARM_MOD IO_FUNCT Assign Parameters to a Module
SFC 58 WR_REC IO_FUNCT Write a Data Record
SFC 59 RD_REC IO_FUNCT Read a Data Record
SFC 60 GD_SND COM_FUNC Send a GD Packet
SFC 61 GD_RCV COM_FUNC Fetch a Received GD Packet
SFC 62 CONTROL COM_FUNC Query the Status of a Connection Belonging to aCommunication SFB Instance
SFC 63 AB_CALL PLASTICS Assembly Code Block (only exists for CPU 614)
SFC 64 TIME_TCK CLK_FUNC Read the System Time
SFC 65 X_SEND COM_FUNC Send Data to a Communication Partner outside the LocalS7 Station
SFC 66 X_RCV COM_FUNC Receive Data from a Communication Partner outside the
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Local S7 Station
SFC 67 X_GET COM_FUNC Read Data from a Communication Partner outside theLocal S7 Station
SFC 68 X_PUT COM_FUNC Write Data to a Communication Partner outside the LocalS7 Station
SFC 69 X_ABORT COM_FUNC Abort an Existing Connection to a CommunicationPartner outside the Local S7 Station
SFC 70 GEO_LOG IO_FUNCT Determine Start Address of a Module
SFC 71 LOG_GEO IO_FUNCT Determine the Slot Belonging to a Logical Address
SFC 72 I_GET COM_FUNC Read Data from a Communication Partner within theLocal S7 Station
SFC 73 I_PUT COM_FUNC Write Data to a Communication Partner within the LocalS7 Station
SFC 74 I_ABORT COM_FUNC Abort an Existing Connection to a CommunicationPartner within the Local S7 Station
SFC 78 OB_RT DIAGNSTC Determine OB program runtime
SFC 79 SET BIT_LOGC Set a Range of Outputs
SFC 80 RSET BIT_LOGC Reset a Range of Outputs
SFC 81 UBLKMOV MOVE Uninterruptible Block Move
SFC 82 CREA_DBL DB_CTRL Create a Data Block in the Load Memory
SFC 83 READ_DBL DB_CTRL Read from a Data Block in Load Memory
SFC 84 WRIT_DBL DB_CTRL Write from a Data Block in Load Memory
SFC 85 CREA_DB DB_FUNCT Create a Data Block
SFC 87 C_DIAG COM_FUNC Diagnosis of the Actual Connection Status
SFC 90 H_CTRL HF_FUNCT Control Operation in H Systems
SFC 100 SET_CLKS CLK_FUNC Setting the Time-of-Day and the TOD Status
SFC 101 RTM CLK_FUNC Handling runtime meters
SFC 102 RD_DPARA IO_FUNCT Redefined Parameters
SFC 103 DP_TOPOL DP Identifying the bus topology in a DP master system
SFC 104 CIR PGM_CNTL Controlling CiR
SFC 105 READ_SI PMC_FUNC Reading Dynamic System Resources
SFC 106 DEL_SI PMC_FUNC Deleting Dynamic System Resources
SFC 107 ALARM_DQ PMC_FUNC Generating Always Acknowledgeable and Block-RelatedMessages
SFC 108 ALARM_D PMC_FUNC Generating Always Acknowledgeable and Block-RelatedMessages
SFC 112 PN_IN PROFIne2 Update inputs in the user program interface of PROFInetcomponents
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SFC 113 PN_OUT PROFIne2 Update outputs in the user program interface ofPROFInet components
SFC 114 PN_DP PROFIne2 Update DP interconnections
SFC 126 SYNC_PI IO_FUNCT Update process image partition input table insynchronous cycle
SFC 127 SYNC_PO IO_FUNCT Update process image partition output table insynchronous cycle
S5-S7 Converting Blocks
Number Name Family Description
FC 61 GP_FPGP S5_CNVRT Change fixed point number to floating point number
FC 62 GP_GPFP S5_CNVRT Change floating point number to fixed point number
FC 63 GP_ADD S5_CNVRT Add floating point numbers
FC 64 GP_SUB S5_CNVRT Subtract floating point numbers
FC 65 GP_MUL S5_CNVRT Multiply floating point number
FC 66 GP_DIV S5_CNVRT Divide floating point numbers
FC 67 GP_VGL S5_CNVRT Compare floating point numbers
FC 68 RAD_GP S5_CNVRT Extract root of floating point numbers
FC 69 MLD_TG S5_CNVRT Clock generator
FC 70 MLD_TGZ S5_CNVRT Clock generator (timing element)
FC 71 MLD_EZW S5_CNVRT Message of first value with single flashing light,wordwise, A
FC 72 MLD_EDW S5_CNVRT Message of first value with double flashing light,wordwise, A
FC 73 MLD_SAMW S5_CNVRT Collected message, wordwise (sound alert)
FC 74 MLD_SAM S5_CNVRT Collected message, bitwise
FC 75 MLD_EZ S5_CNVRT Message of first value with single flashing light, bitwise, A
FC 78 MLD_EDWK S5_CNVRT Message of first value with double flashing light,wordwise, A+M
FC 79 MLD_EZK S5_CNVRT Message of first value with single flashing light, bitwise,A+M
FC 80 MLD_EDK S5_CNVRT Messageof first value with double flashing light, bitwise, A+M
FC 81 COD_B4 S5_CNVRT Change BCD number to 16 bit dual number
FC 82 COD_16 S5_CNVRT Change 16 bit dual number to BCD number
FC 83 MUL_16 S5_CNVRT Multiply 16 bit dual numbers
FC 84 DIV_16 S5_CNVRT Divide 16 bit dual numbers
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FC 85 ADD_32 S5_CNVRT Add 32 bit dual numbers
FC 86 SUB_32 S5_CNVRT Subtract 32 bit dual numbers
FC 87 MUL_32 S5_CNVRT Multiply 32 bit dual numbers
FC 88 DIV_32 S5_CNVRT Divide 32 bit dual numbers
FC 89 RAD_16 S5_CNVRT Extract roots of 16 bit dual numbers
FC 90 REG_SCHB S5_CNVRT Bi-directional shift register, bitwise
FC 91 REG_SCHW S5_CNVRT Bi-directional shift register, wordwise
FC 92 REG_FIFO S5_CNVRT Buffer memory (FIFO)
FC 93 REG_LIFO S5_CNVRT Stack register (LIFO)
FC 94 DB_COPY1 S5_CNVRT Copy data block, direct assignment of parameters
FC 95 DB_COPY2 S5_CNVRT Copy data block, indirect assignment of parameterization
FC 96 RETTEN S5_CNVRT Save scratchpad memory
FC 97 LADEN S5_CNVRT Load scratchpad memory
FC 98 COD_B8 S5_CNVRT Change BCD number to 32 bit dual number
FC 99 COD_32 S5_CNVRT Change 32 bit dual number to BCD number
FC 100 AE_460_1 S5_CNVRT Read analog value
FC 101 AE_460_2 S5_CNVRT Read analog value
FC 102 AE_463_1 S5_CNVRT Read analog value
FC 103 AE_463_2 S5_CNVRT Read analog value
FC 104 AE_464_1 S5_CNVRT Read analog value
FC 105 AE_464_2 S5_CNVRT Read analog value
FC 106 AE_466_1 S5_CNVRT Read analog value
FC 107 AE_466_2 S5_CNVRT Read analog value
FC 108 RLG_AA1 S5_CNVRT Output analog value
FC 109 RLG_AA2 S5_CNVRT Output analog value
FC 110 PER_ET1 S5_CNVRT Read and Write for extended periphery (directassignment of parameters)
FC 111 PER_ET2 S5_CNVRT Read and Write for extended periphery (indirectassignment of parameters)
FC 112 SINUS S5_CNVRT Sine (x)
FC 113 COSINUS S5_CNVRT Cosine (x)
FC 114 TANGENS S5_CNVRT Tangent (x)
FC 115 COTANG S5_CNVRT Cotangent (x)
FC 116 ARCSIN S5_CNVRT Arc sine (x)
FC 117 ARCCOS S5_CNVRT Arc cosine (x)
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FC 118 ARCTAN S5_CNVRT Arc tangent (x)
FC 119 ARCCOT S5_CNVRT Arc cotangens (x)
FC 120 LN_X S5_CNVRT Natural logarithm ln (x)
FC 121 LG_X S5_CNVRT Decade logarithm Iog (x)
FC 122 B_LOG_X S5_CNVRT General logarithm log (x) to basis b
FC 123 E_H_N S5_CNVRT e to the power of n
FC 124 ZEHN_H_N S5_CNVRT 10 to the power of n
FC 125 A2_H_A1 S5_CNVRT AKKU 2 to the power of AKKU 1
IEC Function Blocks
Number Name Family Description
FC 1 AD_DT_TM IEC Point Math Add duration to a time
FC 2 CONCAT IEC Combine two STRING variables
FC 3 D_TOD_DT IEC Combine DATE and TIME_OF_DAY to DT
FC 4 DELETE IEC Delete in a STRING variable
FC 5 DI_STRNG IEC Data type conversion DINT to STRING
FC 6 DT_DATE IEC Extract the DATE from DT
FC 7 DT_DAY IEC Extract the day of the week from DT
FC 8 DT_TOD IEC Extract the TIME_OF_DAY from DT
FC 9 EQ_DT IEC Compare DT for equal
FC 10 EQ_STRNG IEC Compare STRING for equal
FC 11 FIND IEC Find in a STRING variable
FC 12 GE_DT IEC Compare DT for greater than or equal
FC 13 GE_STRNG IEC Compare STRING for greater than or equal
FC 14 GT_DT IEC Compare DT for greater than
FC 15 GT_STRNG IEC Compare STRING for greater than
FC 16 I_STRNG IEC Data type conversion INT to STRING
FC 17 INSERT IEC Insert in a STRING variable
FC 18 LE_DT IEC Compare DT for smaller than or equal
FC 19 LE_STRNG IEC Compare STRING for smaller than or equal
FC 20 LEFT IEC Left part of a STRING variable
FC 21 LEN IEC Length of a STRING variable
FC 22 LIMIT IEC Point Math Limit
FC 23 LT_DT IEC Compare DT for smaller than
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FC 24 LT_STRNG IEC Compare STRING for smaller than
FC 25 MAX IEC Point Math Select maximum
FC 26 MID IEC Middle part of a STRING variable
FC 27 MIN IEC Point Math Select minimum
FC 28 NE_DT IEC Compare DT for unequal
FC 29 NE_STRNG IEC Compare STRING for unequal
FC 30 R_STRNG IEC Data type conversion REAL to STRING
FC 31 REPLACE IEC Replace in a STRING variable
FC 32 RIGHT IEC Right part of a STRING variable
FC 33 S5TI_TIM IEC Data type conversion S5TIME to TIME
FC 34 SB_DT_DT IEC Point Math Subtract two time values
FC 35 SB_DT_TM IEC Point Math Subtract duration from a time
FC 36 SEL IEC Point Math Binary selection
FC 37 STRNG_DI IEC Data type conversion STRING to DINT
FC 38 STRNG_I IEC Data type conversion STRING to INT
FC 39 STRNG_R IEC Data type conversion STRING to REAL
FC 40 TIM_S5TI IEC Data type conversion TIME to S5TIME
PID Control Blocks
Number Name Family Description
FB 41 CONT_C ICONT Continuous Control
FB 42 CONT_S ICONT Step Control
FB 43 PULSEGEN ICONT Pulse Generation
FB 58 TCONT_CP CONTROL Temperature Continuous Controller
FB 59 TCONT_S CONTROL Temperature Step Controller
Communication Blocks
Number Name Family Description
FB 2 IDENTIFY CP_300 For checking deviceproperties
FB 3 READ CP_300 Reads data from a data area of the communicationpartner specified by a name or index depending on theassignment of parameters for the job.
FB 4 REPORT CP_300 Allows unconfirmed transmission of variables by anFMS server.
FB 5 STATUS CP_300 allows status information to be requested from the
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communications partner on the specified FMSconnection.
FB 6 WRITE CP_300 Transfers data from a specified local data area to adata area on the communication partner.
FB 8 USEND CP_300 Uncoordinated Sending of Data
FB 9 URCV CP_300 Uncoordinated Receiving of Data
FB 12 BSEND CP_300 Sending Segmented Data
FB 13 BRCV CP_300 Receiving Segmented Data
FB 14 GET CP_300 Read Data from a Remote CPU
FB 15 PUT CP_300 Write Data to a Remote CPU
FB 20 GETIO IO_FUNCT Read All Inputs of a DP Standard Slave/PROFINET IODevice
FB 21 SETIO IO_FUNCT Write All Outputs of a DP Standard Slave/PROFINET IODevice
FB 22 GETIO_PART IO_FUNCT Read a Part of the Inputs of a DP StandardSlave/PROFINET IO Device
FB 23 SETIO_PART IO_FUNCT Write a Part of the Outputs of a DP StandardSlave/PROFINET IO Device
FB 55 IP_CONFIG CP_300 Transfers a configuration data block (CONF_DB)containing connection data for an Ethernet CP.
FB 63 TSEND COMM Sending Data via TCP native and ISO on TCP
FB 64 TRCV COMM Receiving Data via TCP native and ISO on TCP
FB 65 TCON COMM Establishing a Connection using TCP native and ISO onTCP
FB 66 TDISCON COMM Terminating a Connection using TCP native and ISO onTCP
FB 67 TUSEND COMM Sending Data via UDP
FB 68 TURCV COMM Receiving Data via UDP
FC 1 DP_SEND CP_300 transfers data to the PROFIBUS CP
FC 2 DP_RECV CP_300 receives data on PROFIBUS
FC 3 DP_DIAG CP_300 used to request diagnostic information
FC 4 DP_CTRL CP_300 transfers control jobs to the PROFIBUS CP
FC 5 AG_SEND CP_300 data by means of a configured connection to thecommunication partner (<= 240 bytes).
FC 6 AG_RECV CP_300 data by means of a configured connection from thecommunication partner (<= 240 bytes, not email).
FC 7 AG_LOCK CP_300 the external data access by means of FETCH/WRITE(not for UDP, email).
FC 8 AG_UNLOCK CP_300 the external data access by means of FETCH/WRITE
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(not for UDP, email).
FC 10 AG_CNTRL CP_300 allows you to diagnose connections. When necessary,you can reinitialize connection establishment using theFC.
FC 11 PNIO_SEND CP_300 used for data transfer inthe CP modes PROFINET IO controller or PROFINETIO device.
FC 12 PNIO_RECV CP_300 used to receive data in the CP modes PROFINET IOcontroller or PROFINET IO device.
FC 40 FTP_CONNECT CP_300 Establish an FTP connection
FC 41 FTP_STORE CP_300 Store a file on the FTP server
FC 42 FTP_RETRIEVE CP_300 Retrieve a file from the FTP server
FC 43 FTP_DELETE CP_300 Delete a file on the FTP server
FC 44 FTP_QUIT CP_300 Enable an FTP connection
FC 50 AG_LSEND CP_300 data by means of a configured connection to thecommunication partner.
FC 60 AG_LRECV CP_300 data by means of a configured connection from thecommunication partner (not email).
FC 62 C_CNTRL CP_300 Query a connection status for S7-300
TI-S7 Converting Blocks
Number Name Family Description
FB 80 LEAD_LAG CONVERT Lead/Lag Algorithm
FB 81 DCAT TIMERS Discrete Control Alarm Timer
FB 82 MCAT TIMERS Motor Control Alarm Timer
FB 83 IMC COMPARE Index Matrix Compare
FB 84 SMC COMPARE Scan Matrix Compare
FB 85 DRUM TIMERS Event Maskable Drum
FB 86 PACK MOVE Pack Data
FC 80 TONR TIMERS Software Timer On Delay—Retentive
FC 81 IBLKMOV MOVE Indirect Block Move
FC 82 RSET BIT_LOGC Reset Range of Outputs
FC 83 SET BIT_LOGC Set Range of Outputs
FC 84 ATT TABLE Add to Table
FC 85 FIFO TABLE First In/First Out Unload Table
FC 86 TBL_FIND TABLE Table Find
FC 87 LIFO TABLE Last In/First Out Unload Table
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FC 88 TBL TABLE Table
FC 89 TBL_WRD TABLE Move Table to Word
FC 90 WSR SHIFT Word Shift Register
FC 91 WRD_TBL TABLE Word to Table
FC 92 SHRB SHIFT Bit Shift Register
FC 93 SEG CONVERT Seven Segment Decoder
FC 94 ATH CONVERT ASCII to Hex
FC 95 HTA CONVERT Hex to ASCII
FC 96 ENCO CONVERT Encode Binary Position
FC 97 DECO CONVERT Decode Binary Position
FC 98 BCDCPL CONVERT Ten’s Complement
FC 99 BITSUM CONVERT Sum Number of Bits
FC 100 RSETI BIT_LOGC Reset Range of Immediate Outputs
FC 101 SETI BIT_LOGC Set Range of Immediate Outputs
FC 102 DEV MATH_FP Standard Deviation
FC 103 CDT TABLE Correlated Data Table
FC 104 TBL_TBL TABLE Table to Table
FC 105 SCALE CONVERT Scaling Values
FC 106 UNSCALE CONVERT Unscaling Values
Miscellaneous Blocks
Number Name Family Description
FB 60 SET_SW TIMEFUNC supports the summertime/wintertime changeover in CPUsthat do not have the time status. For this purpose it setsthe CPU clock to the current time and according to thechangeover rules in the Control DB.
FB 61 SET_SW_S TIMEFUNC supports the summertime/wintertime changeover in CPUsthat do have the time status. For this purpose it sets thetime status to the current time and according to thechangeover rules in the Control DB.
FB 62 TIMESTMP TIMEFUNC transfers the time-stamped messages of an IM153-2 intoits instance DB.
FC 60 LOC_TIME TIMEFUNC reads the time status or time of the CPU and calculates thelocal time. It is therefore only useful on CPUs with timestatus.
FC 61 BT_LT TIMEFUNC calculates the local time from the base time given at theinput.
FC 62 LT_BT TIMEFUNC calculates the base time from the local time given at the
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input.
FC 63 S_LTINT TIMEFUNC sets the required time interrupt to the preset time. Thistime is given in local time.
Siemens Technical Terms
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Siemens Technical TermsOtherwise known as Siemens speak. Here's a list of Siemens specific abbreviations and theirmeanings.
Term Description Explanation
C7 Combo PLC/HMI system A PLC and screen in one package
CFC Continuous FunctionChart Optional programming language
CP CommunicationProcessor Modules used for special communication protocols
DB Data Block Memory storage areas for user data
FB Function Block A function with it's own data block
FBD Function Block Diagram Standard programming language
FC Function Call Called progammed blocks
FM Function Module Modules with special functions (e.g. positioning)
GSD Generic StationDescription Files used for Profibus descriptions
HiGraph Optional programming language
IM Interface Module Modules to connect remote racks
LAD Ladder Logic Diagram Standard programming language
M7 Programmable modules A module with processing capabilities
MMC Micro Memory Card Compact plug-in memory card
MPI Multi Point Interface Standard communication protocol
OB Organization Block Blocks for user programs based on different operatingsystem events.
OP Operator Panel Simple display with or without buttons
PCS Process Control System Software for the entire process chain
PG Programming Terminal Dedicated Siemens device - basically a PC
PPI Point to Point Interface Serial RS-232 communication
ProfibusDP
Profibus DecentralPeripherals Networking protocol used for factory automation
ProfibusPA
Profibus ProcessAutomation Networking protocol used for process automation
S7 SIMATIC Step 7 product line
Structured Control
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SCL Language Optional programming language
SFB System Function Block Integrated FB for CPU information
SFC System Function Call Integrated FC for CPU information
SM Signal Module Standard Input/Output modules
STL Statement List Text based programming language
TP Touch Panel Touch screen display
UDT User-Definded DataType Special data structures defined by the user
VAT Variable Access Table Tables used to monitor/modify values in the PLC
Step 7 Elementary Data Types
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Step 7 Elementary Data TypesType andDescription
SizeinBits
FormatOptions
Range and NumberNotation(lowest to highest values)
Example in STL
BOOL (Bit) 1 Booleantext
TRUE/FALSE TRUE
BYTE (Byte) 8 Hexadecimalnumber
B#16#0 to B#16#FF L B#16#10L byte#16#10
WORD(Word)
16 Binarynumber
2#0 to2#1111_1111_1111_1111
L 2#0001_0000_0000_0000
Hexadecimalnumber
W#16#0 to W#16#FFFF L W#16#1000L word#16#1000
BCD C#0 to C#999 L C#998
Decimalnumberunsigned
B#(0,0) to B#(255,255) L B#(10,20)L byte#(10,20)
DWORD(Doubleword)
32 Binarynumber
2#0 to2#1111_1111_1111_1111_1111_1111_1111_1111
L 2#1000_0001_0001_1000_1011_1011_0111_1111
Hexadecimalnumber
W#16#0000_0000 toW#16#FFFF_FFFF
L DW#16#00A2_1234L dword#16#00A2_1234
Decimalnumberunsigned
B#(0,0,0,0) toB#(255,255,255,255)
L B#(1, 14, 100, 120)L byte#(1,14,100,120)
INT(Integer)
16 Decimalnumbersigned
-32768 to 32767 L 101
DINT(Doubleinteger)
32 Decimalnumbersigned
L#-2147483648 toL#2147483647
L L#101
REAL(Floating-pointnumber)
32 IEEEFloating-pointnumber
Upper limit +/-3.402823e+38Lower limit +/-1.175495e-38
L 1.234567e+13
S5TIME(SIMATICtime)
16 S7 time insteps of10ms(default)
S5T#0H_0M_0S_10MS toS5T#2H_46M_30S_0MS andS5T#0H_0M_0S_0MS
L S5T#0H_1M_0S_0MSLS5TIME#0H_1H_1M_0S_0MS
TIME (IECtime)
32 IEC time insteps of 1ms, integersigned
T#24D_20H_31M_23S_648MStoT#24D_20H_31M_23S_647MS
L T#0D_1H_1M_0S_0MSL TIME#0D_1H_1M_0S_0MS
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DATE (IECdate)
16 IEC date insteps of 1day
D#1990-1-1 toD#2168-12-31
L D#1996-3-15L DATE#1996-3-15
TIME_OF_DAY(Time)
32 Time insteps of 1ms
TOD#0:0:0.0 toTOD#23:59:59.999
L TOD#1:10:3.3L TIME_OF_DAY#1:10:3.3
CHAR(Character)
8 ASCIIcharacters
A', 'B' etc. L 'E'
S5TIME NOTES
Underscores in time and date are optionalIt is not required to specify all time units (for example: T#5h10s is valid)Maximum time value = 9,990 seconds or 2H_46M_30S
S5TIME Format
Time base Binary Code
10 ms 00
100 ms 01
1 s 10
10 s 11
Symbol Table Allowed Addresses and Data Types
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Symbol Table Allowed Addresses and DataTypesEnglish Mnemonics
German Mnemonics Description Data Type Address
Range
I/O Signals
I E Input bit BOOL 0 to65535.7
IB EB Input byte BYTE, CHAR 0 to 65535
IW EW Input word WORD, INT, S5TIME,DATE 0 to 65534
ID ED Input double word DWORD, DINT, REAL,TOD, TIME 0 to 65532
Q A Output bit BOOL 0 to65535.7
QB AB Output byte BYTE, CHAR 0 to 65535
QW AW Output word WORD, INT, S5TIME,DATE 0 to 65534
QD AD Output double word DWORD, DINT, REAL,TOD, TIME 0 to 65532
Marker Memory
M M Memory bit BOOL 0 to65535.7
MB MB Memory byte BYTE, CHAR 0 to 65535
MW MW Memory word WORD, INT, S5TIME,DATE 0 to 65534
MD MD Memory double word DWORD, DINT, REAL,TOD, TIME 0 to 65532
Peripheral I/O
PIB PEB Peripheral input byte BYTE, CHAR 0 to 65535
PIW PEW Peripheral input word WORD, INT, S5TIME,DATE 0 to 65534
PID PED Peripheral input doubleword
DWORD, DINT, REAL,TOD, TIME 0 to 65532
PQB PAB Peripheral output byte BYTE, CHAR 0 to 65535
PQW PAW Peripheral output word WORD, INT, S5TIME,DATE 0 to 65534
PQD PAD Peripheral output DWORD, DINT, REAL, 0 to 65532
Symbol Table Allowed Addresses and Data Types
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double word TOD, TIME
Timers and Counters
T T Timer TIMER 0 to 65535
C Z Counter COUNTER 0 to 65535
Logic Blocks
FB FB Function block FB 0 to 65535
OB OB Organization block OB 1 to 65535
FC FC Function FC 0 to 65535
SFB SFB System function block SFB 0 to 65535
SFC SFC System function SFC 0 to 65535
Data Blocks
DB DB Data block DB, FB, SFB, UDT 1 to 65535
User-defined data types
UDT UDT User-defined data type UDT 0 to 65535
Siemens S7 Indirect Addressing
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Siemens S7 Indirect Addressingby Automation Training
The following is provided by Automation Training from their excellent Siemens Step 7 trainingmanual. This is a really nice explanation of a difficult but important subject. Check out theirwebsite for hands-on and online training classes.
Introduction
The most common form of addressing used in the Siemens S7 PLCs is direct and symbolic.When a direct addressed is referenced by an instruction there is no question as to the locationin memory. The following are examples of direct addressing:
Inputs: I4.0, IB4, IW4 , ID4
Outputs: Q124.0, QB124, QW124, QD124
Markers: M11.0, MB10, MW10, MD10
Timers: T34
Counters: C23
Local: L0.0, LB1, LW2, LD4
Data Block: DB5.DBX2.0, DB5.DBW6, DBD8
By using the methods of indirect addressing the address used by an instruction can be varied topoint to any number of locations. In this case, a memory location stores a “pointer†toanother memory location. While this may increase the difficulty of troubleshooting, itsadvantage is to greatly reduce the number of networks and instructions needed to control aprocess. It is also a method that must be understood to use some of the library and systemfunction calls provided by Siemens.
The POINTER and ANY Data Types
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A POINTER data type is used to format a number to be accepted as an address rather then avalue. A pointer is always preceded by a P# symbol. The pointer address may be in threedifferent formats.
Format Example Memory Storage
P#<byte>.<bit> P#8.0P#124.3
4 Bytes
P#<area><byte>.<bit> P#M50.0P#I4.0
6 Bytes
P#<area><byte>.<bit><length> P#DB25.DBX0.0 BYTE 14P#M0.0 WORD 2P#I0.0 DWORD 5
10 Bytes
The ANY data type is used to pass a parameter of an unknown or undefined data type. Somefunctions in the library use the ANY data type to work on whole sections of memory. To dothis, the last pointer method is used to describe an area. For example the address P#DB25.DBX0.0 Byte 14 points to the first byte of DB25 with a length of 14 bytes.
NOTE: A DINT can be converted to a POINTER by simply shifting the double word left by 3 bits.
Data Block Instructions
When working with indirect addressing it is sometimes needed to first of all open a DB and thenbegin working on theaddress without directly referring to any one DB. This is done using the OPN instruction. TheOPN instruction can open either a shared data block (DB) or an instance data block (DI).
OPN DB 10 //Open DB10 as a shared data block
L DBW 36 //Load data word 36 of DB10 into ACCU1
T MW 22 //Transfer the contents of ACCU1 into MW22
OPN DI 20 //Open DB20 as an instance data block
L DIB 12 //Load data byte 12 from DB20 into ACCU1
T DBB 37 //Transfer the contents of ACCU1 to data//byte 37 of the open shared data block DB10
When monitoring in STL the shared DB number is displayed in the DB1 column and theinstance DB number is displayed in the DB2 column.
Furthermore, there are instructions to confirm that the correct DB number is opened and that itis large enough for the next operation.
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L DBNO //Loads the number of the opened //shared data block into ACCU1
L DBLG //Loads the length of the opened//shared data block into ACCU1
L DINO //Loads the number of the opened//instance data block into ACCU1
L DILG //Loads the length of the opened//instance data block into ACCU1
Memory Indirect Addressing
The first method of indirect addressing is called memory indirect addressing because it allowsfor a memory location (M, DB or L) to determine or point to another.
The memory area identifiers T, C, DB, DI, FB and FC use a word (16-bit) pointer location ininteger format. Two examples are as follows:
L 5 //Load ACCU1 with pointer value
T MW 2 //Transfer pointer into MW2
L T [MW 2] //Load ACCU1 with T5 current time value
OPN DB [#DB_Temp] //Open DB whose data block number is //from the interface temp parameter //named DB_Temp
The memory area identifiers I, Q, M, L, DB use a double word (32-bit) location using thePOINTER data type.
L P#0.7 //Load ACCU1 with pointer value
T MD 2 //Transfer pointer into MD2
A I [MD 2] //Check state of I0.7
= M [MD 2] //Assign value of RLO to M0.7
OPN DB 5 //Open DB5
L P#2.0 //Load pointer into ACCU1
T #TempPointer //Transfer pointer to temp location
L DBW [#TempPointer] //Load the value at DB5.DBW2 into ACCU1
L 0 //Load a zero into ACCU1
>D //Check if the value is greater //then zero
When monitoring memory indirect addressing the INDIRECT column displays the currentaddress the instruction is using.
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Note that math can be done on the POINTER data type using the double math instructions(e.g. P#2.0 + P#5.0 = P#7.0).
L P#2.0 //Load ACCU1 with pointer value
L P#5.0 //Load ACCU1 with secondpointer value
+D
T MD 0 //MD0 now contains the value P#7.0
Since the bit position only goes to eight the result of P#8.7 + P#1.1 = P#10.0 and not P#9.8.These methods can be used to offset the address or increase/decrease the pointer in a loop.
The Address Registers
Besides the regular accumulators, there are two 32-bit address registers (AR1, AR2) for storingpointers used in register indirect addressing methods. A series of different load and transfertype instructions can be used to work with AR1. A similar set is available for AR2.
STL Description
LAR1 Loads AR1 with the contents of ACCU1
LAR1 P#M100.0 Loads AR1 with a pointer constant
LAR1 MD24 Loads AR1 with the pointer in MD24
LAR1 AR2 Loads AR1 with the contents of AR2
TAR1 Transfers the contents AR1 into ACCU1
TAR1 MD28 Transfers the contents in AR1 to a memory location
TAR1 AR2 Transfers the contents in AR1 to AR2
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CAR Exchanges the contents of AR1 with AR2
Addition can be directly accomplished on AR1 and AR2 with the following:
STL Description
+AR1 Adds the contents of ACCU1 to AR1 and stores the result back intoAR1
+AR1 P#100.0 Adds the pointer constant to AR1 and stores the result back into AR1
Area-Internal Register Indirect Addressing
The area-internal register indirect addressing method uses one of the address registers plus apointer to determine the address the instruction is to reference. The format is:
address identifier [address register, pointer]
The address identifier can be I, Q, M, L, DI or DB in bit, byte, word or double word form. Theaddress register must be previously loaded with a double word pointer without reference to theaddress identifier. The exact address is determined by adding the address register with thepointer. The example below shows the area-internal method using bit locations.
L P#0.7 //Load ACCU1 with pointer value
LAR1 //Load AR1 with pointer in ACCU1
A I [AR1, P#0.0] //Check input I0.7
= Q [AR1, P#1.1] //If RLO=1 turn on Q2.0
Area-Crossing Register Indirect Addressing
Area-crossing register indirect addressing is similar to the area-internal method except thepointer loaded into the address register references a memory area (e.g. P#M10.0 orP#DBX0.0). This means the address identifier used before the opening bracket is not needed ifreferencing a bit otherwise it will be a B for byte, W for word or D for double. The examplebelow shows the area-crossing method using bit locations.
L P#I0.7 //Load ACCU1 with pointer value
LAR1 //Load AR1 with pointer in ACCU1
L P#Q124.0 //Load ACCU1 with pointer value
LAR2 //Load AR2 with pointer in ACCU1
A [AR1, P#0.0] //Check input I0.7
= [AR2, P#1.1] //If RLO=1 turn on Q125.1
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This next example shows area-crossing methods using a word and double word format.
L P#M0.0 //Load ACCU1 with pointer value
LAR1 //Load AR1 with pointer in ACCU1
L W [AR1,P#10.0]
//Load the word whose address is //determined by the contents of //AR1 plus 10 bytes (MW10) into ACCU1
OPN DB 5 //Open DB5
L P#DBX 0.0 //Load ACCU1 with pointer value
LAR2 //Load AR2 with pointer in ACCU1
L L#0 //Load zero into ACCU1
T D [AR2,P#50.0]
//Transfer the value in ACCU1 to the //double word whose exact location is //the address in AR2 plus 50 bytes //(DB5.DBD50)
Exercise #1
1. Comment the lines of STL below to describe what this network does:
A I 0.0
JC M001
L P#M10.0
JU M002
M001: L P#Q0.0
M002: LAR1
A I 0.1
= [AR1, P#0.1]
2. Enter the code, monitor it and verify your answers.
Exercise #2 (Advanced)
1. Create a DB with an array of 10 real numbers. Populate the array with random values.2. Create a function that will return the max number in the array and its position. Use the
indirect addressing method of your choice.
Siemens S7 Status Word
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Siemens S7 Status WordIn Siemens PLCs the Status Word is an internal CPU register used to keep track of the state ofthe instructions as they are being processed. In order to use STL more effectively it isimportant to understand the Status Word and its functions.
Each bit in the Status Word has a specific function to keep track of bit logic (RLO, STA), math(OV, OS), comparison operations (CC0, CC1) and whether the logic should continue, be nestedor start new (/FC, OR, BR). Only the first 9 of the 16 bits are used.
Bit Positions
8 7 6 5 4 3 2 1 0
BR CC0 CC1 OV OS OR STA RLO /FC
Each instruction may do the following to each bit in the status word.
- No read or write
* Read
x May write "1" or "0"
0 Reset to "0"
1 Set to "1"
The status word can be seen by displaying the STATUS column while monitoring in STL view. The RLO (bit 1) and the STA (bit 2) are also displayed in the RLO and STA column.
The Most Important Status Word Bits
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/FC – First Check (bit 0)
If the /FC bit is a 0 then the instruction is considered to be the first instruction beingprocessed. If the /FC is a 1 then the instruction being scanned will use the logic from theprevious instruction. Certain instructions like =, S and R will set the /FC bit to 0 thus startingnew logic after it. Other instructions like A or O will set the /FC bit to 1 signalling to combinethe logic with the next instruction.
RLO – Result of Logic Operation (bit 1)
The RLO bit stores the running logic state of the currently processing instructions. Certain bitlogic and comparison instruction will turn the RLO to a 1 when the condition is TRUE and writea 0 when the condition is FALSE. Other instructions read the RLO (=, S, R) to determine howthey are to execute.
STA – Status (bit 2)
The STA bit reflects the state of the current Boolean address.
Help with RLO, STA and /FC
If you are used to ladder logic and struggling to understand the purpose of the RLO and STA itmay help to visualize a rung like below. The STA is used to keep track of the state of theaddresses. The RLO is used to keep track of the state of the rung.
The equivalent STL is shown below.
It steps through the logic as follows:
1. At the start the First Check bit (/FC) is zero so an And instruction will logically mirror theStatus bit (STA) over to the Result of Logic Operation (RLO). In this case the addressI0.0 is 1 so the STA is one and the result of the logic (RLO) will be 1. The A instructionwrites a 1 to /FC.
Siemens S7 Status Word
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2. On the second line, the /FC bit is now 1 indicating that this line needs to use the RLOfrom the previous line. The address I1.1 is on so the STA = 1. The RLO from the lastline is 1 and this is ‘anded’ with the current STA with a result of 1 in the currentRLO.
3. The same thing happens on the second line but this time 1 and 0 makes the current RLO= 0.
4. The fourth is the Assign instruction which takes the RLO and writes it out to thecorresponding address. In this case the final RLO = 0 so the output will be off. IfM0.0 was 1 then the “And†operation will evaluate to true making the RLO = 1 whichwill then turn on the output Q1.0.
The Other Status Bits
OR (bit 3)
The OR bit is used for combining AND functions before OR functions.
OS – Overflow Stored (bit 4)
In the event of an overflow (OV bit 5) the OS bit will store the value even after the OV bit hasbeen reset. The following commands reset the OS bit: JOS (Jump if OS=1), block callinstructions, block end instructions.
OV – Overflow (bit 5)
The OV bit is set by a math instruction with floating point numbers after a fault has occurred(overflow, illegal operation, comparison unordered). The OV bit is reset when the fault iseliminated.
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CC0, CC1 – Condition Code (bits 6 and 7)
The Condition Code bits provide results for comparison and math instructions.
Comparison Instructions
CC 1 CC 0 Meaning
0 0 ACCU 2 = ACCU 1
0 1 ACCU 2 < ACCU 1
1 0 ACCU 2 > ACCU 1
1 1 Unordered (floating point comparison only)
Math Instructions, without Overflow
CC 1 CC 0 Meaning
0 0 Result = 0
0 1 Result < 0
1 0 Result > 0
Integer Math Instructions, with Overflow
CC 1 CC 0 Meaning
0 0 Negative range overflow in ADD_I and ADD_DI
0 1 Negative range overflow in MUL_I and MUL_DI
1 0 Negative range overflow in ADD_I, ADD_DI, SUB_I, and SUB_DI
1 1 Division by 0 in DIV_I, DIV_DI, and MOD_DI
Floating Point Math Instructions, with Overflow
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CC 1 CC 0 Meaning
0 0 Gradual underflow
0 1 Negative range overflow
1 0 Positive range overflow
1 1 Not a valid floating-point number
Shift and Rotate Instructions
CC 1 CC 0 Meaning
0 0 Bit shifted out = 0
1 0 Bit shifted out = 1
Word Logic Instructions
CC 1 CC 0 Meaning
0 0 Result = 0
1 0 Result <> 0
BR – Binary Result (bit 8)
The Binary Result transfers the result of the operationsonto the next instruction for reference. When the BR bit is 1 it enables the outputof the block (ENO) to be TRUE and thus allow other blocks after it to beprocessed. The SAVE, JCB and JNB instructions set the BR bit.