Modbus RTU vs Modbus TCP: choosing between RS-485 and Ethernet I/O
How RS-485 and Ethernet I/O differ in cabling, scan time and addressing, how to combine them with gateways, and which ICP DAS series fit.
Win-GRAF soft PLC: IEC 61131-3 programming on an ICP DAS PAC
What Win-GRAF PACs are, which IEC 61131-3 languages and I/O options they offer, and when a PAC makes more sense than a classic PLC.
Published
A soft PLC runs IEC 61131-3 control programs on an industrial computer instead of on dedicated PLC hardware. ICP DAS offers this as Win-GRAF PACs: programmable automation controllers with the Win-GRAF runtime built in. This article explains what a Win-GRAF soft PLC is, which languages and engineering functions it offers, how I/O is added, and when a PAC is a better choice than a classic PLC.
What a Win-GRAF soft PLC is
Each Win-GRAF PAC combines a CPU, an operating system and an embedded Win-GRAF SoftLogic runtime. The control program is written on a PC in the Win-GRAF Workbench, downloaded to the PAC and executed there in cycles, as on a PLC. The operating system depends on the family: Windows CE 7.0 on the WP-5238-CE7, WP-8x28-CE7 and WP-9x28-CE7, Windows CE 6.0 on the XP-8x38-CE6, Windows 10 IoT Enterprise on the XP-9xx8-IoT, and Linux with the Xenomai real-time core on the RPAC-2658M.
Because the PAC has a full operating system, other software can run next to the control program. The Windows CE models support applications written in VB.NET or C# with Visual Studio 2008, which exchange data with the Win-GRAF application, for example for an HMI or data management. For machines built around a PC, the Win-GRAF PC Runtime turns a standard or industrial Windows PC into a soft PLC. It is supplied with a USB dongle, and the Workbench is not included in that package.
Languages and engineering functions
The Win-GRAF Workbench supports all five languages defined in IEC 61131-3:
- Ladder diagram (LD) for discrete logic that electricians can follow
- Function block diagram (FBD) for signal flow and control loops
- Structured text (ST) for calculations, loops and data handling
- Sequential function chart (SFC) for step sequences
- Instruction list (IL), mainly for existing code, since the third edition of the standard marks it as deprecated
Several languages can be used in one project, a program can be converted into another language, and two versions of a project can be compared. Tasks run with priority settings, and reusable code can be kept in user libraries.
The PAC runtime adds functions that matter during commissioning and operation: online change, retain variables, schedule control, data binding, file access and data logging, and application protection. On the communication side, the PACs list OPC UA server, Modbus TCP master and slave, Modbus RTU master and slave, DCON and user-defined protocols for serial devices.
I/O expansion: local slots and remote modules
Most Win-GRAF PACs have slots for ICP DAS PAC I/O modules, so the controller and its local I/O form one DIN-rail unit. The WP-8x28-CE7 and XP-8x38-CE6 take I-8K parallel and I-87K serial modules, the WP-9x28-CE7 and XP-9xx8-IoT take I-9K and I-97K modules, and the compact WP-5238-CE7 uses an XV-board expansion board. The table below gives the slot counts.
Remote I/O is connected through the serial and Ethernet ports. As a Modbus RTU master the PAC can poll M-7000 or tM modules on RS-485, as a Modbus TCP master it can read ET-7000, ET-7200 or ET-2200 modules, and the DCON support covers the I-7000 series. A machine can then use local I/O for signals in the main cabinet and distributed I/O close to sensors and actuators.
For motion, ICP DAS also has Win-GRAF based EtherCAT controllers with PLCopen function blocks. The EMP-2848M controls up to 128 EtherCAT slaves and 16 axes at cycle times down to 500 µs, and the EMP-9xx8 series handles up to 32 axes at a 0.5 ms cycle time.
Which Win-GRAF PAC fits
| Family | Operating system | CPU | Local I/O | Notes |
|---|---|---|---|---|
| WP-5238-CE7 | Windows CE 7.0 | Cortex-A8, 1 GHz | XV-board | Compact, 4 serial ports, 12 to 48 VDC supply |
| WP-8x28-CE7 | Windows CE 7.0 | Cortex-A8, 1 GHz | 1, 4 or 8 slots, I-8K/I-87K | VGA output, redundant power inputs |
| WP-9x28-CE7 | Windows CE 7.0 | Cortex-A8, 1 GHz | 2, 4 or 8 slots, high-profile I-9K/I-97K | Metal case, VGA output |
| XP-8x38-CE6 | Windows CE 6.0 | x86 dual-core, 1 GHz | 0, 1, 3 or 7 slots, high-profile I-8K/I-87K | Dual-PAC redundancy |
| XP-9xx8-IoT | Windows 10 IoT Enterprise, 64-bit | Intel Atom E3845 | 1, 3 or 7 slots, I-9K/I-97K | VGA and HDMI, dual-PAC redundancy |
| RPAC-2658M | Linux with Xenomai | Cortex-A9 quad-core, 1 GHz | Remote I/O over Modbus or DCON | 3 Gigabit Ethernet ports, dual-PAC redundancy |
| ViewPAC VP-1238/4238/6238-CE7 | Windows CE 7.0 | Cortex-A8, 1 GHz | 3 slots, high-profile I-8K/I-87K | 5.7, 10.4 or 15 inch display, IP65 front panel |
When a PAC makes sense instead of a classic PLC
A Win-GRAF PAC is programmed like a PLC, so the choice is less about the control logic and more about what else the controller has to do. A PAC is a good fit when:
- Control and data handling belong in one device, such as logging to files, a local SQL database on the Windows CE models, or OPC UA for an MES.
- The machine talks to many devices on different ports and protocols, including serial instruments with their own protocol.
- An operator interface is needed on the controller itself, through the VGA output with eLogger HMI or on a ViewPAC with a built-in display.
- Custom software in C# or VB.NET has to share data with the control program.
- Controller redundancy is required, using the dual-PAC redundancy of the XP-8x38-CE6, XP-9xx8-IoT or RPAC-2658M.
A classic PLC is often the simpler choice when the plant standard prescribes a PLC platform and its engineering tools, or when maintenance staff are trained only on that platform. Safety functions need a controller or relay that is certified for that purpose, whichever platform runs the rest of the machine.
Users of older ISaGRAF PACs should note that ICP DAS states ISaGRAF cannot run on 64-bit Windows 7 and 8 PCs and points to Win-GRAF as the alternative.
Send technical sales a short description of the machine, its I/O count and the protocols involved, and we will suggest a suitable Win-GRAF PAC and I/O modules.
Products for this application
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I-8014W-G CR
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353,00 EUR
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I-8017DW-G CR
I-8017DW-G Analog Input Module, 8/16-ch, 14-bit, 100 kHz, DB37 Connector
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