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System Operation
5. SYSTEM SECURITY
Security in the Alspa C80–35 and Alspa C80–25 PLCs is designed to prevent unauthorized changes to the contents
of a PLC. There are four security levels available in the PLC. The first level, which is always available, provides
only the ability to read PLC data; no changes are permitted to the application. The other three levels have access
to each level protected by a password. The information in this paragraph is also applicable to the Alspac C80–05
Micro PLC.
Each higher privilege level permits greater change capabilities than the lower level(s). Privilege levels accumulate
in that the privileges granted at one level are a combination of that level, plus all lower levels. The levels and their
privileges are:
Privilege Level
Description
Level 1
Any data, except passwords may be read. This includes all data memories (%I, %Q, %AQ, %R, etc), fault
tables, and all program block types (data, value and constant). No values may be changed in the PLC.
Level 2
This level allows write access to the data memories (%I, %R, etc).
Level 3
This level allows write access to the application program in STOP mode only.
Level 4
This is the default level for systems which have no passwords set. The default level for a system with
passwords is to the highest unprotected level. This level, the highest, allows read and write access to all
memories as well as passwords in both RUN and STOP mode. (Configuration data cannot be changed
in RUN mode.)
5.1.
Passwords
There is one password for each privilege level in the PLC. (No password can be set for level 1 access.) Each
password may be unique; however, the same password can be used for more than one level. Passwords are one to
four ASCII characters in length; they can only be entered or changed with the Alspa P8–25/35/05 software or the
Hand–Held Programmer.
A privilege level change is in effect only as long as communications between the PLC and the programmer are
intact. There does not need to be any activity, but the communications link must not be broken. If there is no
communication for 15 minutes, the privilege level returns to the highest unprotected level.
Upon connection of the PLC, the Alspa P8–25/35/05 programmer requests the protection status of each privilege
level from the PLC. The Alspa P8–25/35/05 programmer then requests the PLC to move to the highest unprotected
level, thereby giving the programmer access to the highest unprotected level without having to request any
particular level. When the Hand–Held Programmer is connected to the PLC, the PLC reverts to the highest
unprotected level.
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Alspa C80–35, C80–25 and C80–05 PLCs Reference Manual
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