Table of Contents
How to Reset CPU Memory
First put CPU in stop mode by putting selector switch on stop position. Put selector switch in MRES position and hold for sometime to allow stop LED blink slowly. Put selector switch back in stop position and suddenly put back to MRES position and finally back to stop position. Stop LED will blink fastly first and then will stop. It indicates that CPU memory is reset.
This method will reset all variable values of memory and not the entire program saved in Load Memory.
To delete all data in the memory, we need to go into S7 software and selecting all data blocks and pressing delete key.
PLC Interface Module (IM)
Total number of modules of S7-300 PLC that can be placed in one rack is 11. If we exceed from 11 then we need to put other extra modules on second rack.
Interface Module is used to connect/interface these two racks. We need two IM, first on rack-1 and second on rack-2.
Types of Electrical Signals
Signal is a physical quantity that varies with time. There are two types of electrical signals used widely in industry.
- Digital Signal (ON or OFF)
- Analog Signal
Digital Input and Digital Output (DI and DO) Modules
These module gets digital signals (Zero or One) as input and CPU processes these signals according to given program. After processing these signals are sent to digital output modules and perform output.
Analog Input and Analog Output (AI and AO) Modules
Similarly, AI modules inputs analog quantity like temperature and convert it to processable data which is given to CPU for processing. CPU process this data and perform required result based processing to give command to AO module.
Function Module (FM)
If we need high accuracy results/processing of any signal (like speed), we cannot connect it with regular DI or AI module because these modules are not accurate much high as required in speed regulation. So, we need function modules which process data independently and not need main CPU for processing.
FM receives data and convert it in processable data. After that it process it and convert to electrical signal which will be sent to output facility.
Communication Processor (CP) Modules
If we have two CPUs and two IM modules in the same facility, we can connect each CPU to the IM module through the Profibus DP network.
Suppose we also need to communicate between two CPUs at the same time. Then, this cannot be connected because there is only one DP port in each CPU.
Here, the CP module comes into the party to solve this problem.
We will put two CP modules next to each CPU and connect them using a DP port through a Profibus cable.
FAQs for “Class-3: Best SIEMENS PLC S7-300 Course using new TIA Portal (CPU Memory)”
1. How do I reset the CPU memory of the S7-300 PLC?
- To reset the CPU memory, you need to place the CPU in stop mode, switch to the MRES position, hold until the stop LED blinks, and then switch back to stop mode. This will reset all variable values but will not delete the program stored in Load Memory.
2. What is the function of the Interface Module (IM) in the S7-300 PLC?
- The Interface Module (IM) connects two racks in the S7-300 PLC system, allowing for expansion beyond the limit of 11 modules in a single rack. Up to three racks can be expanded using IM modules.
3. What is the difference between Digital Input (DI) and Analog Input (AI) modules in the S7-300 PLC?
- Digital Input (DI) modules handle binary signals (ON/OFF), while Analog Input (AI) modules process analog signals, such as temperature or pressure, converting them into data that the CPU can process.
4. When do I need to use a Function Module (FM) in the S7-300 PLC?
- A Function Module (FM) is required for high-accuracy processing tasks, like speed regulation, where standard DI or AI modules may not provide the required precision. The FM processes the data independently of the CPU.
5. How can I enable communication between two CPUs in an S7-300 PLC system?
- To connect two CPUs for communication, a Communication Processor (CP) module is used. CP modules connect the CPUs via a Profibus DP port, enabling data exchange between them.
