134
Digitax HD M753 Control User Guide
Issue Number: 3
11 Onboard PLC
11.1
Onboard PLC and Machine Control
Studio
The drive has the ability to store and execute a 16 kB Onboard PLC user
program without the need for additional hardware in the form of an
option module.
Machine Control Studio is an IEC61131-3 development environment
designed for use with Digitax HD and compatible application modules.
All of the programming languages defined in the IEC standard
IEC 61131-3 are supported in the Machine Control Studio development
environment.
•
ST (Structured text)
•
LD (Ladder diagram)
•
FBD (Function block diagram)
•
IL (Instruction list)
•
SFC (Sequential function chart)
•
CFC (Continuous Function Chart). CFC is an extension to the
standard IEC programming languages
Machine Control Studio provides a complete environment for the
development of user programs. Programs can be created, compiled and
downloaded to a Digitax HD for execution, via the communications port
on the front of the drive. The run-time operation of the compiled program
on the target can also be monitored using Machine Control Studio and
facilities are provided to interact with the program on the target by setting
new values for target variables and parameters.
The Onboard PLC and Machine Control Studio form the first level of
functionality in a range of programmable options for Digitax HD.
Machine Control Studio can be downloaded from www.drive-setup.com.
See the Machine Control Studio help file for more information regarding
using Machine Control Studio, creating user programs and downloading
user programs to the drive.
11.2 Benefits
The combination of the Onboard PLC and Machine Control Studio,
means that the drive can replace nano and some micro PLCs in many
applications Machine Control Studio benefits from access to function
and function block libraries as well as those from third parties. Functions
and function blocks available as standard in Machine Control Studio
include, but not limited to, the following:
•
Arithmetic blocks
•
Comparison blocks
•
Timers
•
Counters
•
Multiplexers
•
Latches
•
Bit manipulation
Typical applications for the Onboard PLC include:
•
Ancillary pumps
•
Fans and control valves
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Interlocking logic
•
Sequences routines
•
Custom control words.
11.3 Features
The Digitax HD M Onboard PLC user program has the following
features:
11.3.1
Tasks
The Onboard PLC allows use of two tasks.
•
Clock: A high priority real time task. The clock task interval can be
set from 4 ms to 262 s in multiples of 4 ms. The parameter
Onboard
User Program: Clock Task Time Used
(11.051) shows the
percentage of the available time used by clock task. A read or write
of a drive parameter by the user program takes a finite period of
time. It is possible to select up to 10 parameters as fast access
parameter which reduced the amount of time it takes for the user
program to read from or write to a drive parameter. This is useful
when using a clock task with a fast update rate as selecting a
parameter for fast access reduces the amount of the clock task
resource required to access parameters.
•
Freewheeling: A non-real time background task. The freewheeling
task is scheduled for a short period once every 64 ms. The time for
which the task is scheduled will vary depending on the loading of the
drive's processor. When scheduled, several scans of the user
program may be performed. Some scans may execute in
microseconds. However, when the main drive functions are
scheduled there will be a pause in the execution of the program
causing some scans to take many milliseconds. The parameter
Onboard User Program: Freewheeling Tasks Per Second
(11.050)
shows the number of times the freewheeling task has started per
second.
11.3.2
Variables
The Onboard PLC supports the use of variables with the data types of
Boolean, integer (8 bit, 16 bit and 32 bit, signed and unsigned), floating
point (64 bit only), strings and time.
11.3.3
Custom menu
Machine Control Studio can construct a custom drive menu to reside in
menu 30 on the drive. The following properties of each parameter can
be defined using Machine Control Studio:
•
Parameter name
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Number of decimal places
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The units for the parameter to be display on the keypad.
•
The minimum, maximum and default values
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Memory handling (i.e. power down save, user save or volatile)
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Data type. The drive provides a limited set of 1 bit, 8 bit, 16 bit and
32 bit integer parameters to create the customer menu.
Parameters in this customer menu can be accessed by the user
program and will appear on the keypad.
11.3.4
Limitations
The Onboard PLC user program has the following limitations:
•
The flash memory allocated to the Onboard PLC is 16 kB which
includes the user program and its header which results in a
maximum user program size of about 12 kB
•
The Onboard PLC is provided with 2 kB of RAM.
•
The drive is rated for 100 program downloads. This limitation is
imposed by the flash memory used to store the program within the
drive.
•
There is only one real-time task with a minimum period of 4 ms.
•
The freewheeling background task runs at a low priority. The drive is
prioritized to perform the clock task and its major functions first, e.g.
motor control, and will use any remaining processing time to execute
the freewheeling task as a background activity. As the drive's
processor becomes more heavily loaded, less time is spent
executing the freewheeling task.
•
Breakpoints, single stepping and online program changes are not
possible.
•
The Graphing tool is not supported.
•
The variable data types REAL (32 bit floating point), LWORD (64 bit
integer) and WSTRING (Unicode string), and retained variables are
not supported.
11.4 Onboard
PLC
parameters
The following parameters are associated with the Onboard PLC user
program.
This parameter stops and starts the user program.
11.047
Onboard User Program: Enable
RW
Txt
US
Stop (0) or Run (1)
Run (1)
Summary of Contents for Digitax HD M753 EtherCAT
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