I have the same problem like you ,

DEAR SIR, i have done all that mentioned by you.i replace the MMC card by another one and i put the protection as you say to me .i put it in the first one . Just i have make a little change in the program and when i try to redownload the program again in the cpu . it suggests a password another time.!!!!!!!!.  i guess that the password is in the cpu not in the MMC card .what shall i do more ?? SHALL I reset the cpu also  ?

PLEASE ANSWER ME AS SOON AS POSSIBLE.

AutoGen_3750966

I have the same problem like you ,

DEAR SIR, i have done all that mentioned by you.i replace the MMC card by another one and i put the protection as you say to me .i put it in the first one . Just i have make a little change in the program and when i try to redownload the program again in the cpu . it suggests a password another time.!!!!!!!!.  i guess that the password is in the cpu not in the MMC card .what shall i do more ?? SHALL I reset the cpu also  ?

PLEASE ANSWER ME AS SOON AS POSSIBLE.

Hello,

Witch cpu that you have ? 

AutoGen_3750966

cpu314c PN/DP

 hi,

yes you can reset the CPU to factory-settings. After this reset there is no password-protection on the cpu and no programm is on it any more.

In this manual you will find the procedure in chapter 9.5:

SIMATIC S7-300 CPU 31xC and CPU 31x: Installation

manual, page 197

Proceed as follows in order to reset a CPU to the delivery state via the mode selector switch:
1. Switch off the supply voltage.
2. Remove the SIMATIC Micro Memory Card from the CPU.
3. Hold the mode selector switch in the MRES setting and switch the supply voltage on
again.
4. Wait until LED lamp image 1 from the subsequent overview is displayed.
5. Release the mode selector switch, set it back to MRES within 3 seconds and hold it in
this position.
6. Wait until LED lamp image 2 from the next overview is displayed.
This lamp image lights up for approximately five seconds, that is for the duration of
RESET. During this period you can abort the resetting procedure by releasing the mode
selector switch.
7. Wait until LED lamp image 3 from the subsequent overview is displayed and release the
mode selector switch again.
The CPU is now reset to the delivery state. It starts without buffering (all LEDs are lit) and
changes to the STOP mode.

 hope this helps,

regards,