PLC programming differs from other computer software programming. A written program doesn't run automatically on a computer; it requires external circuitry and mechanical equipment to realize its value. This is a characteristic of automation technology: theory plus practice, and the integration of hardware and software, is the correct direction for automation development. Today, we've summarized several ways to connect a PLC to a computer.
1. Serial port
Serial port is the earliest and most convenient method. It establishes a connection between the computer's built-in serial port and the PLC's serial port. Early PLCs all used this download method. Examples include the Mitsubishi FX series, Siemens S7-200, and S7-300 series. Even in the new century, many computers have eliminated serial ports, but very few PLCs do not have them.
The serial port of a PLC is generally used to establish a connection with a touch screen. Modern computers no longer have serial ports; instead, USB-to-serial cables are typically used, especially USB-to-485 serial cables, which are widely used not only for PLCs but also for connecting various frequency converters and servo drives. Don't assume that frequency converters and servo drives only have a few parameters and don't need to be connected. When troubleshooting load problems, it's essential to connect and monitor the frequency converter's parameters and various statuses.
USB to RS485 is a staple tool for industrial control engineers. For example, when performing serial communication, we can use a serial port assistant to monitor data. This cable can replace the download cable for early Siemens S7-200 PLCs, and it's also compatible with many frequency converters, servo drives, and any download cable that uses RS485 communication. Original cables are generally very expensive; using a universal USB to RS485 cable can save considerable costs.
The connection cables for Siemens S7-200, GE PLCs of various series, Danfoss, CT, Fuji, Schneider, Lenze and other drives can all be replaced with USB to 485 cables, while their original cables are extremely expensive.
2. USB
While serial ports offer many advantages, they also have several drawbacks, the biggest being their slow speed. With technological advancements, USB has gradually gained widespread adoption. Modern PLCs all support USB programming, with the most common interface being the MicroUSB port, the T-shaped connector found in older mobile phones and external hard drives. Not only PLCs, but also most touchscreens and text displays use this interface for program downloading.
As shown in the image above, this is a Mitsubishi FX3 series PLC. Notice the interface circled in red; many industrial control products use this type of interface. Almost all touchscreens use this download interface.
Another type of interface is the square USB interface, which is the same interface on the printer. Omron PLCs use this interface, so the printer's connection cable is the Omron PLC's download cable.
As shown in the picture above, the part circled in red is the download interface of the Omron PLC, which is the same as the printer interface.
Serial port and USB are two of the most common connection methods, suitable not only for PLCs but also widely used in touch screens, servo drives, frequency converters, and many other applications. Many PLCs support both connection methods simultaneously.
As shown in the image above, this is the connection option of Mitsubishi PLC programming software GXWORKS2. We can see that it supports two modes.
3. Network cable
With the development of internet technology, Ethernet is increasingly being used in industrial automation. Therefore, many PLCs now support wired network connections, such as Siemens' latest TIA Portal platform, the S7-1200 series. Even the lower-end S7-200 Smart series supports Ethernet port connections.
In summary, some people in the industrial control field are very wise: by learning one product, they can apply their knowledge to other products; by solving one problem, they can find solutions to other problems. While it's important to know how many brands of products you're familiar with and how many instructions you memorize, the most crucial thing is to apply your knowledge flexibly and think in different ways.
Understanding the principles and basics, and grasping the essence of various connection methods, will save you a lot of unnecessary trouble and achieve twice the result with half the effort.
