s71200_getting_started_en-US_en-US (1)

Use a watch table for monitoring 5

When you tested the latching circuit (Page 38), you used the physical switch
on the simulator and watched the lights turn on and off on the front of the
CPU.

For this exercise, you will use the online functionality of STEP 7 Basic to
monitor the operation of your user program.

What is a "watch table"?

A watch table allows you to monitor or modify the values of tags while the CPU executes
your user program.

The "Modify" function allows you to change the value of a tag.
However, the "Modify" function does not work with inputs (I) or
outputs (Q) because the CPU updates the I/O, overwriting any
modified value before reading the modified value.

The watch table provides a "Force" function that allows you to
modify the values of the I/O. For this exercise, you will learn how
to force the input in the latch circuit on.

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Use a watch table for monitoring
5.1 Create a watch table

5.1 Create a watch table

To create a watch table:

1. Expand the "Watch tables" container.

2. Double-click "Add new watch table" to open a new
watch table.

Enter the tags by clicking in the "Name" field. Type a character and select the tag from the
list.

After you create your watch table, you can go online to monitor the
execution of your user program.

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Use a watch table for monitoring
5.2 Monitor the data values in your CPU

5.2 Monitor the data values in your CPU

To monitor the tags, you must have an online connection to
the CPU. Simply click the "Go online" button in the toolbar.

When you have connected to the CPU, STEP 7 Basic turns the
headers of the work areas orange.
The project tree displays a comparison of the offline project and
the online CPU. A green circle means that the CPU and the project
are synchronized, meaning that both have the same configuration
and user program.
The watch table shows the tags.

To monitor the execution of the user program and to display the values of the tags,
click the "Monitor all" button in the toolbar. The "Monitor value" field shows the value
for each tag.

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Use a watch table for monitoring
5.3 Monitor the status in the LAD editor

5.3 Monitor the status in the LAD editor

You can also monitor the status of the tags in the LAD editor. Use the editor bar to display
the LAD editor. The editor bar allows you to change the view between the open editors
without having to open or close the editors.

Click the LAD editor.

In the toolbar of the LAD editor, click the "Monitoring on/off" button to display the
status of your user program.

The LAD editor displays power
flow in green.

With all of the switches on the simulator turned off, notice that the "On" input is not green
because it is off (or "false"). Notice also that there is no power flow going to the "Off"
contact. However, the normally closed contact "Off" itself is green. "Off" being green does
not in itself generate power flow, but means that if power were to flow into the "Off" contact,
then the power flow would be passed on to the "Run" coil.
Using the simulator, turn the switch for I0.0 on and watch the power flow across the
network. Now, turn I.0.0 off and see how the latching circuit works!

Now turn the switch for I0.1 off to
remove power flow from the "Run"
coil (Q0.0).

5.4 Force an input to a specific value

A watch table provides a "force" function that overwrites the value for an input or output
point to a specified value for the peripheral input or peripheral output address. The CPU
applies this forced value to the input process image prior to the execution of the user
program and to the output process image before the outputs are written to the modules.

Use the editor bar to open the watch table.
Because you cannot force an input (or "I" address), you must change the address for "On"
input to access the peripheral input. In the "Address" or "Name" cell for "On", append a ":P"
to the address ("On:P").

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Use a watch table for monitoring
5.4 Force an input to a specific value

Now click the "Show/hide force columns" button to display the "Force value" column.

Right-click the "Force value" cell to display the context menu. Select the "Force to 1"
command to set "On:P" (I0.0) to 1 or "true".

Because the force values are stored in
the CPU and not in the watch table,
STEP 7 Basic asks you to confirm
setting the force value to 1. Click "Yes"
to confirm.

Use the "Start or replace forcing" button to force the value of the "On:P" input to 1
(or "true"). Click the "Stop forcing" button to reset the value of "On:P" to 0 (or
"false").

With all of the switches on the simulator turned off, notice that the when "On:P" is 0
("false"), the "Run" output remains "true" (1 or on).

Note
When an input or output is forced in a watch table, the force actions become part of the user
program. If you close STEP 7 Basic, the forced elements remain active for the user program
being executed by the CPU program until they are cleared. To clear these forced elements,
you must use STEP 7 Basic to connect with the online CPU and use the watch table to turn
off or stop the force function for those elements.

Now click the "Go offline" button to disconnect
from the CPU.

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5.5 Going online

5.5 Going online

One last bit of information deals with the CPU operator panel. Remember that the CPU
does not provide a physical switch for changing modes from STOP to RUN. You use
STEP 7 Basic to change the operating mode for the CPU.
First, you access the online CPU.

1. Expand the "Online access" folder and expand the
network adapter that connects to the CPU.

2. Double-click "Update accessible nodes" to find your
CPU.

3. After STEP 7 Basic displays the CPU, expand the CPU.
4. Double-click "Online & diagnostics" to display the online

tools.

The "Online tools" task card provides a variety of tools for monitoring the performance of
the CPU, such as the diagnostic buffer, measurements of scan time and memory usage,
and the CPU operating panel.

Use the CPU operator panel to change the operating mode.
Click the "RUN" or "STOP" buttons to change the operating
mode of the CPU.
Be careful! Clicking the "MRES" button performs a memory
reset and deletes the work memory of the CPU! (While the
MRES does not delete the user program, the non-retentive
memory areas are set to the default configuration for the CPU.)

5.6 Building on a good beginning

Congratulations on having gotten started with your S7-1200 CPU and the STEP 7 Basic
programming software!

There is more to learn, but you should now have a foundation in the
skills you need to start creating your own projects.
Refer to the S7-1200 Easy Book and the S7-1200 Programmable
Controller System Manual. These manuals contain useful
information that explains the capabilities of the S7-1200.
Don't forget to check out the customer support web site
(http://www.siemens.com/automation/support-request) for FAQs and
other types of useful documentation.

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Index

A D

AND logic, 14, 31 Data types, 11
Appearance of STEP 7, 24 Deleting networks, 47
Detect CPU, 23, 35
B Dimensions, 26
Discover CPU, 23, 35
Basic electrical circuits Displaying the contents and index (online help), 19
bridge circuit, 16 Documentation, 19
change-over switch, 16 Drag and drop
diode circuit, 16
between editors, 22
Bit memory (M), 7 between LAD networks, 47
Branch for a network, 31 from Instruction task card, 42
instructions, 21
C
E
Changing settings for STEP 7, 24
Changing the tag address, 47 Electrical circuits
Circuit diagrams bridge circuit, 16
change-over switch, 16
bridge circuit, 16 diode circuit, 16
change-over switch, 16
convert to LAD, 13, 14 Ethernet communication, 28
diode circuit, 16
CPU F
bit memory (M), 7
connecting power, 27 Favorites toolbar, 21, 31
data types, 11 Force, 54
force, 54
inputs and outputs, 7 I memory, 54
load memory, 7 peripheral inputs, 54
M memory, 7
monitoring, 53 G
MRES, 56
number of timers and counters supported, 41 Guidelines for installation, 25, 26
online, 53
operating modes, 9, 56 H
operator panel, 9, 56
overview, 7 Help, 19
physical size, 7, 26 Displaying the contents and index, 19
process image, 7 Expanding, 19
program execution, 8 Printing, 20
retentive memory, 7 Undocking, 19
safety guidelines, 25, 26
saving, 32, 34, 37, 44, 46, 48 57
unspecified CPU, 23, 35
work memory, 7

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Index MRES, 56

I M

I memory, 12 M memory, 7
address peripheral inputs, 54 changing tags, 47
changing tags, 47 enter addresses, 42
enter addresses, 33 tags, 42
force, 54
monitor, 53 Memory areas, 7
tags, 33 address peripheral inputs, 54
watch table, 53, 54 I memory, 12
M memory, 12
Information system, 19 peripheral I/O, 12
Displaying the contents and index, 19 process image, 12
Printing, 20 Q memory, 12
Undocking, 19
Memory reset (MRES), 9, 56
Input simulator Monitoring
installing, 27
testing with, 38 create a watch table, 52
force, 54
Inputs and outputs, 7, 12 LAD status, 53
forcing, 54 watch table, 52, 53, 54
monitoring, 53
scan cycle, 8 N

Installation, 26, 27, 28 Network
safety guidelines, 25, 26 add branch, 31
deleting networks, 47
Instructions
changing the address of an instruction, 47 Number of timers and counters supported by S7-
coil, 31 1200, 41
contacts, 31
drag and drop between editors, 22 O
editing networks, 47
favorites, 21, 31 Off-delay (TOF) instruction, 44
force, 54 On-delay (TON) instruction, 41
inserting, 21, 31 Online
Instruction task card, 45
monitor, 53 connecting, 56
new branch, 31 force, 54
status, 53, 54 MRES, 56
TOF (off-delay timer), 44 operator panel, 9, 56
TON (on-delay timer), 41 watch table, 53
Online help, 19
L Displaying the contents and index, 19
Expanding the help window, 19
LAD Printing, 20
convert from a circuit diagram, 13, 14 Undocking, 19
edit instructions, 47 Operating mode, 8, 9, 56
insert instructions, 31, 42, 45 Operator panel, 9, 56
monitor, 53 OR logic, 14, 31
new branch, 31
status, 53, 54 Getting started with S7-1200
tags, 33 Getting Started, 11/2009, A5E02486791-01

Latch circuit, 31
LEDs, 7
Load memory, 7

58

P S Index
59
Physical size, 26 S7-1200
PLC force, 54
monitoring, 53
bit memory (M), 7 MRES, 56
data types, 11 operator panel, 56
force, 54 physical size, 26
inputs and outputs, 7 safety guidelines, 25, 26
load memory, 7 saving, 32, 34, 37, 44, 46, 48
M memory, 7
monitoring, 53 Safety guidelines, 25, 26
MRES, 56 Saving, 32, 34, 37, 44, 46, 48
number of timers and counters supported, 41 Saving the project, 31
overview, 7 Scan cycle, 8
physical size, 7, 26
process image, 7 force, 54
program execution, 8 Settings for STEP 7, 24
retentive memory, 7 Simulator
saving, 32, 34, 37, 44, 46, 48
unspecified CPU, 23, 35 installing, 27
work memory, 7 testing with, 38
Portal view, 18 Starting STEP 7 Basic, 28
Printing the help topics, 20 STARTUP mode
Process image, 7, 12 force, 54
force, 54 program execution, 8
monitor, 53 Status LEDs, 7
status, 53, 54 STEP 7
PROFINET, 28 data types, 11
Programming detect CPU, 23, 35
deleting networks, 47 force, 54
drag and drop between editors, 22 installation, 28
editing, 47 languages, 24
favorites, 21 monitoring, 53
program execution, 8 MRES, 56
Project view, 18 operator panel, 9, 56
Portal view, 18
Q Project view, 18
saving, 32, 34, 37, 44, 46, 48
Q memory, 12 settings, 24
changing tags, 47 starting, 28
tags, 33 watch table, 52
STOP mode, 9, 56
R force, 54

Retentive memory, 7 T
RUN mode, 9, 56
Tags
force, 54 changing the address, 47
program execution, 8 force, 54
I memory, 33
Getting started with S7-1200 M memory, 42
Getting Started, 11/2009, A5E02486791-01 monitor, 53
status, 53, 54
tag table, 33, 47

Index

TIA Portal User interface
Portal view, 18 Portal view, 18
Project view, 18 Project view, 18

Timers W
number of timers and counters supported, 41
TOF (on-delay), 44 Watch table
TON (on-delay), 41 create, 52
force, 51, 54
Transform a circuit diagram, 13, 14 monitor, 51, 53

U Work memory, 7

Unspecified CPU, 23, 35
Upload, 35

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