How does PLC use time to stop working for a certain period of time and release the password?

Programmable Logic Controller (PLC) is a digital computing controller with a microprocessor for automatic control. It can load control instructions into memory at any time for storage and execution. The programmable controller consists of CPU, instruction and data memory, input/output interface, power supply, digital analog conversion and other functional units. The early programmable logic controller only had the function of logic control, so it was named programmable logic controller. Later, with the continuous development, these computer modules with simple functions at the beginning have various functions including logic control, timing control, analog control, multi-machine communication, etc., and the name was changed to programmable controller (PLC). However, because its abbreviation PC conflicts with the abbreviation of personal computer (Personal Computer), and because of habit, people still often use the name of programmable logic controller and still use the abbreviation PLC.

How to use time to stop working in PLC and enter password to unlock it. This function is generally used for collecting final payment or installment payment of purchased equipment. When the equipment is used for a certain period of time, the equipment will be locked and a specific password needs to be entered to unlock it. It usually needs to be used in conjunction with the touch screen to complete.

The touch screen can be divided into password input and password release. If you enter the password, you will continue to have the right to use it as shown in the figure below, and you will need to pay the fee when it expires. To release the password, you need to pay the final payment in one lump sum to completely release the password permission. This can be set according to the manufacturer's requirements, such as entering the password once every six months.

If we use PLC to set passwords and stop the equipment, we will eventually have to set PLC output prohibition. The next step is how to design the time, whether to calculate according to working hours or according to dates. We use half a year as the deadline. There are many ways to set the program as shown in the following figure. According to the special soft element M8014 (1-minute clock signal), it is converted into days. As long as the equipment is turned on, the time will be counted. If the number of days exceeds half a year, M8034 will be set to prohibit all PLC outputs. The password for the half-year output period will be released. If the time is continued until the deadline of one year, another password needs to be entered. If it is divided into multiple periods, multiple passwords need to be set. The data register for timing uses the cumulative power-off preservation type. If the release period password is entered, the above two passwords will become invalid, and the PLC output prohibition function will be deleted at the same time.

If the date is used for setting, it needs to be set according to the factory date of the device. For example, if the device is shipped in March 2019, then the first expiration date of the device is September, and the second expiration date is March of the following year. The password is the same as the above setting as shown in the following procedure:

If someone has your source program or cracks it, the password will naturally be known if this encryption program is set up for PLC. It will be safer if encryption is performed in conjunction with a touch screen. In many cases, when equipment like this is sold, the full amount is not paid and there is always some balance. Setting this encryption is purely helpless.