Siemens Simatic S7-200 System Manual page 57

Recovering from a Lost Password
If you forget the password, you must clear the memory of the S7-200 and reload your program. Clearing
the memory puts the S7-200 in STOP mode and resets the S7-200 to the factory-set defaults, except for
the network address, baud rate, and the time-of-day clock. To clear your program in the S7-200:
1. Select the PLC > Clear menu command to display the Clear dialog box.
2. Select all three blocks and confirm your action by clicking OK.
3. If a password had been configured, STEP 7–Micro/WIN displays a password-authorization dialog
box. To clear the password, enter CLEARPLC in the password-authorization dialog box to continue
the Clear All operation. (The CLEARPLC password is not case sensitive.)
The Clear All operation does not remove the program from a memory cartridge. Since the memory
cartridge stores the password along with the program, you must also reprogram the memory cartridge to
remove the lost password.
Warning
Clearing the S7-200 memory causes the outputs to turn off (or in the case of an analog output, to be
frozen at a specific value).
If the S7-200 is connected to equipment when you clear the memory, changes in the state of the outputs
can be transmitted to the equipment. If you had configured the "safe state" for the outputs to be different
from the factory settings, changes in the outputs could cause unpredictable operation of your
equipment, which in turn could cause death or serious injury to personnel, and/or damage to equipment.
Always follow appropriate safety precautions and ensure that your process is in a safe state before
clearing the S7-200 memory.
The S7-200 Provides Analog Adjustment Potentiometers
The analog adjustment potentiometers are located under the front access cover of the module. You can
adjust these potentiometers to increase or decrease values that are stored in bytes of Special Memory
(SMB). These read-only values can be used by the program for a variety of functions, such as updating
the current value for a timer or a counter, entering or changing the preset values, or setting limits. Use a
small screwdriver to make the adjustments: turn the potentiometer clockwise (to the right) to increase the
value, and counterclockwise (to the left) to decrease the value.
SMB28 holds the digital value that represents the position of analog adjustment 0. SMB29 holds the digital
value that represents the position of analog adjustment 1. The analog adjustment has a nominal range of
0 to 255 and a repeatability of ±2 counts.
Sample Program for Referencing the Value Entered with the Analog Adjustment Potentiometers
Network 1 //Read analog adjustment 0 (SMB28).
//Save the value as an integer in VW100.
LD I0.0
BTI SMB28, VW100
Network 2 //Use the integer value (VW100) as a preset for a timer.
LDN Q0.0
TON T33, VW100
Network 3 //Turn on Q0.0 when T33 reaches the preset value.
LD T33
= Q0.0
PLC Concepts Chapter 4
45
4