The CPU, or Central Processing Unit, is the core component of a PLC (Programmable Logic Controller) system. It controls and executes the user program based on its current operating mode. The front panel of the CPU includes two LEDs that indicate the working status: a green LED indicates that the CPU is in RUN mode, meaning it is actively executing the program, while a red LED indicates that the CPU is in STOP mode, where no program execution occurs. If the SF (System Fault) indicator is lit, it means the system has detected an error, and the PLC will stop functioning until the issue is resolved. 1. How the CPU Works (1) STOP Mode: When the CPU is in STOP mode, it does not execute any program. This mode is used for programming, downloading, or modifying the program. During these operations, the CPU must be set to STOP to ensure proper configuration. This allows users to edit the logic, upload new programs, or adjust settings without interference from ongoing execution. (2) RUN Mode: In RUN mode, the CPU runs the user program according to its internal scan cycle. This involves reading input signals, executing the logic, and updating output signals. This mode is typically used during normal operation when the PLC is controlling the connected devices. 2. Ways to Change the Working Mode (1) Using the Mode Switch: Most CPUs have a physical switch that allows users to change the operating mode. The switch usually has three positions: STOP, TERM (Terminal), and RUN. By setting the switch to STOP, the program execution halts. Setting it to RUN resumes program execution. The TERM position allows communication with programming software like STEP7-Micro/WIN32, enabling real-time monitoring and control. Upon power-up, if the switch is in STOP or TERM, the CPU automatically enters STOP mode. If set to RUN, it starts in RUN mode. (2) Using Programming Software: With the mode switch set to TERM, users can change the CPU’s operating mode through the STEP7-Micro/WIN32 software. This method is useful for remote control or when more advanced configurations are required. (3) Using Instructions in the Program: A STOP instruction inserted into the program can force the CPU to transition from RUN to STOP mode. This is often used for emergency stops or controlled shutdowns during program execution. P03 Series Push Wire Connectors
Smaller size, space saving
Fast connection
111
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Model
CPU221
CPU222
CPU224
CPU226
CPU226MX
User Data Storage Type
EEPROM
EEPROM
EEPROM
EEPROM
EEPROM
Program Space (Permanently Saved)
2048 words
2048 words
4096 words
4096 words
8192 words
User Data Storage
1024 words
1024 words
2560 words
2560 words
5120 words
Data Backup (Super Capacitor) - Typical Value / H
50
50
190
190
190
Host I/O Points
6/4
8/6
14/10
24/16
24/16
Scalable Module
No
2
7
7
7
24V Sensor Power Supply Max Current / Current Limit (mA)
180/600
180/600
280/600
400/1500
400/1500
Maximum Analog Input/Output
No
16/16
28/7 or 14
32/32
32/32
240V AC Power Supply CPU Input Current / Max Load Current (mA)
25/180
25/180
35/220
40/160
40/160
24V DC Power Supply CPU Input Current / Max Load (mA)
70/600
70/600
120/900
150/1050
150/1050
DC5V Output for Expansion Module
-
Max 340mA
Max 660mA
Max 1000mA
Max 1000mA
Built-in High Speed Counter
4 (30KHz)
4 (30KHz)
6 (30KHz)
6 (30KHz)
6 (30KHz)
High Speed Pulse Output
2 (20KHz)
2 (20KHz)
2 (20KHz)
2 (20KHz)
2 (20KHz)
Analog Adjustment Potentiometer
1
1
2
2
2
Real Time Clock
Yes (Clock Card)
Yes (Clock Card)
Have (Built In)
Have (Built In)
Have (Built In)
RS-485 Communication Port
1
1
1
1
1
Number of Points per Group
4,2
4,4
8,6
13,11
13,11
Output Points per Group
4 (DC Power)
1,3 (AC Power)
6 (DC Power)
3,3 (AC Power)
5,5 (DC Power)
4,3,3 (AC Power)
8,8 (DC Power)
4,5,7 (AC Power)
8,8 (DC Power)
4,5,7 (AC Power)