S7-300 there are many different types of CPU, suitable for different levels of control. CPU module is integrated with the digital I/O, and integrated digital I/O and analog I/O.
CPU component is packaged in a sturdy and compact plastic enclosure, Panel on the status and error indicator LED, mode selection switch and communication interfaces. Micro memory card slot you can insert up to several megabytes of FEPROM micro memory card (MMC), after loss of program and data preservation. Some CPU, only one MPI interface.
1. Status and fault indication LED
CPU module Panel for LED (light emitting diode) the meaning of
CPU in RUN mode RUN LED lit; 2Hz frequency during boot shining; HOLD State with 0.5Hz frequency lights. When CPU is STOP, HOLD or restart STOP LED Permanent; request a memory reset to 0. 5Hz frequency blinking are the memory reset to 2Hz frequency lights.
2. CPU operation mode
1) STOP (stop) mode: the mode selector switch is in the STOP position, automatically enters STOP mode after power on the CPU module, which does not execute user program can receive global data and checking the system.
2) RUN (run) mode: execute user programs, refresh the input and output, handling interrupts and faults information services.
3) HOLD mode: start and RUN mode when debugging with breakpoints, the user program execution is suspended (paused), the timer is frozen.
4) STARTUP (boot) model: you can use the mode selector switch or STEP 7 start the CPU. If the mode select switch is in the RUN position, power on automatically when entering the start mode.
5) old CPU key to switch to select the operation mode, it also has a RUN-P mode, allows to read and modify the program at runtime. Simulation software simulation of the PLCSIM CPU RUN-P mode, certain monitoring functions can only be carried out in RUN-P mode.
3. Mode selector switch
CPU mode selector switch to the position of significance are as follows:
1) RUN (run): CPU execute user programs.
2) STOP (stop): CPU not execute user programs.
3) MRES (memory reset): MRES position cannot be maintained in this position when you let go the switch will automatically return to the STOP position. From the STOP position to pull the mode selection switch into the MRES position, can reset the memory, the CPU back to the initial state. Working memory and S7-400 of RAM loaded in memory user program and address area is cleared, all memory, timers, counters and data block is reset to zero, including the data hold function. CPU hardware, initializing the hardware and system parameters, system parameters, CPU and is restored to the default settings of the parameters of the module, MPI (multi point interface) parameter is reserved. CPU inside the MMC after the reset of the user programs and system parameters are copied to the storage area.
Reset memory operations in the following order: PLC power from the STOP position to pull the mode selection switch into the MRES position, STOP LED extinguished 1s, 1s, went out again after 1s remain on. Release the switch and make it return to the STOP position. 3S to pull to the MRES position, STOP the frequency flashing at least 3s LED 2Hz, said it is a reset, finally STOP LED on, reset the end, you can release the mode selector switch.
4. Communication interface
All CPU modules have a MPI (multi point interface) communication interfaces, some CPU module with PROFIBUS-DP interface or a point to point interface, model PN CPU modules in an industrial Ethernet PROFINET interfaces.
MPI interface is used with other Siemens PLC, PG/PC (programmer or a PC), OP (operator panel) through the MPI network communications.
PROFIBUS-DP can be used with other Siemens PLC, PG/PC, OP and other DP master and slave communications.
5. Power terminal blocks
The power supply module L+ and m terminals DC 24V output voltage anode and cathode, respectively. Use dedicated power connector or wires connected to the power supply module and the L+ CPU module, and m terminals.