Operating and display elements   
2.2 Operating and display elements: CPU 31x 
  CPU 31xC and CPU 31x, Technical Data 
2-8  Manual, 01/2006 Edition, A5E00105475-06 
Slot for the SIMATIC Micro Memory Card (MMC)  
Memory module is a SIMATIC Micro Memory Card. You can use MMCs as load memory and 
as portable storage medium.  
 
 
 
Note 
These CPUs do not have an integrated load memory and thus require a SIMATIC Micro 
Memory Card for operation. 
 
Mode selector switch 
Use the mode selector switch to set the CPU operating mode.  
Table 2-4  Mode selector switch settings 
Position  Meaning  Description 
RUN  RUN mode  The CPU executes the user program. 
STOP  STOP mode  The CPU does not execute a user program. 
MRES  CPU memory reset  Mode selector switch position with pushbutton function for CPU 
memory reset. A CPU memory reset by means of mode 
selector switch requires a specific sequence of operation. 
Reference 
•  CPU operating modes: 
STEP 7 Online Help.
 
•  Information on CPU memory reset:
 Operating instructions CPU 31xC and CPU31x, 
Commissioning, Commissioning Modules, CPU Memory Reset by means of Mode 
Selector Switch
 
•  Evaluation of the LEDs upon error or diagnostic event:
 Operating Instructions CPU 31xC 
and  
CPU 31x, Test Functions, Diagnostics and Troubleshooting, Diagnostics with the help of 
Status and Error LEDs
 
Power supply connection 
Each CPU is equipped with a double-pole power supply socket. The connector with screw 
terminals is inserted into this socket when the CPU is delivered.