108
Digitax ST User Guide
Issue: 5
11 Onboard PLC
11.1 Onboard PLC and SYPTLite
The Digitax ST has the ability to store and execute a 4KB Onboard PLC
ladder logic program without the need for additional hardware.
The ladder logic program is written using SYPTLite, a Windows™ based
ladder diagram editor allowing the development of programs for
execution in Digitax ST.
SYPTLite is designed to be easy to use and to make program
development as simple as possible. The features provided are a sub-set
of those in the SYPT program editor. SYPTLite programs are developed
using ladder logic, a graphical language widely used to program PLCs
(IEC61131-3). SYPTLite allows the user to "draw" a ladder diagram
representing a program.
SYPTLite provides a complete environment for the development of
ladder diagrams. Ladder diagrams can be created, compiled into user
programs and downloaded to a Digitax ST for execution, via the RJ45
serial communications port on the front of the drive. The run-time
operation of the compiled ladder diagram on the target can also be
monitored using SYPTLite and facilities are provided to interact with the
program on the target by setting new values for target parameters.
11.2 Benefits
The combination of the Onboard PLC and SYPTLite, means that Digitax
ST can replace nano and some micro PLCs in many applications. The
Onboard PLC programs can consist of up to a maximum of 50 ladder
logic rungs (up to 7 function blocks and 10 contacts per rung). The
Onboard PLC program can also be transferred to and from a
SMARTCARD for backup or quick commissioning / start-up
In addition to the basic ladder symbols, SYPTLite contains a sub-set of
the function from the full version of SYPT. These include,
•
Arithmetic blocks
•
Comparison blocks
•
Timers
•
Counters
•
Multiplexers
•
Latches
•
Bit manipulation
Typical applications for the Onboard PLC include,
•
Interlocking logic
•
Sequences routines
•
Custom control words.
11.3 Limitations
The Onboard PLC program has the following limitations:
•
The maximum program size is 4032 bytes including header and
optional source code.
•
The Digitax ST is rated for 100 program downloads. This limitation is
imposed by the flash memory used to store the program within the
drive.
•
The user cannot create user variables. The user is only able to
manipulate the drive parameter set.
•
The program cannot be downloaded or monitored over CTNet. The
program is only accessible via the drives RJ45 serial
communications port.
•
There are no real-time tasks, i.e. the scheduling rate of the program
cannot be guaranteed. SM-Applications tasks such as Clock, Event,
Pos0 or Speed are not available. The Onboard PLC should not be
used for time-critical applications.
•
The program runs at a low priority. The Digitax ST provides a single
background task in which to run a ladder diagram. The drive is
prioritized to perform its major functions first, e.g. motor control, and
will use any remaining processing time to execute the ladder
diagram as a background activity. As the drive's processor becomes
more heavily loaded, less time is spent executing the program.
Figure 11-1 Digitax ST Onboard PLC program scheduling
The user program is scheduled for a short period approximately once
every 64 ms. The time for which the program is scheduled will vary
between 0.2 ms and 2 ms 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. SYPTLite
displays the average execution time calculated over the last 10 scans of
the user program.
11.4 Getting started
SYPTLite can be downloaded at: http://www.emersonindustrial.com/en-
EN/controltechniques/products/software/programming/syptlite/Pages/
default.aspx.
SYPTLite system requirements
•
Windows 2000/XP/Vista.
Windows 95/98/98SE/Me/NT4 are not
supported
•
Pentium III 500 MHz or better recommended
•
128 MB RAM
•
Minimum of 800x600 shield resolution. 1024x768 is recommended
•
Adobe Acrobat 5.10 or later (for viewing User Guides)
•
Microsoft Internet Explorer V5.0 or later
•
RS232 to RS485, RJ45 communications lead to connect the PC to a
Digitax ST
•
Administrator rights under Windows NT/2000/XP/Vista are required
to install the software
See the SYPTLite help file for more information regarding using
SYPTLite, creating ladder diagrams and the available function blocks.
11.5 Onboard PLC parameters
The following parameters are associated with the Onboard PLC
program.
This parameter is used to start and stop the drive Onboard PLC program.
11.47
Drive Onboard PLC program enable
RW
Uni
US
Ú
0 to 2
Ö
2
Value
Description
0
Halt the drive Onboard PLC program.
1
Run the drive Onboard PLC program (if installed). Any out-of-
range parameter writes attempted will be clipped to the
maximum / minimum values valid for that parameter before
being written.
2
Run the drive Onboard PLC program (if installed). Any out-of-
range parameter writes attempted will cause a ‘UP ovr’ trip.
Major drive
functions
User
program
0
64
128
Time
(milliseconds)
Summary of Contents for Digitax ST
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