2-4 Series 90™-70 Enhanced Hot Standby CPU Redundancy User's Guide May 2000 GFK-1527A
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CPU Features

Memory Protect Keyswitch

The Memory Protect keyswitch can be used to manually
lock program and configurati on data from access by a
remote programmer (serial or Ethernet). When the key is
in the ON position , program and con fi guration data can
only be changed by a programmer connected to the Bus
Transmitter Module.

CPU LEDs

OK: The OK LED is ON when the CPU is functioning properly. The

OK LED blinks when the CPU executes power-up diagnostics, when
the remote unit is powered-up, or if the system has failed. If the system
has failed and the OK LED is blinking, the CPU can still communicate
with the programmer (the CPU cann ot communicate with the
programmer during power-up diagnostics). If the OK LED is OFF, the
system has failed and the CPU cannot communicate with the
programmer.

RUN: This LED is ON when the CPU is in the RUN/ENABLE or RUN/DISABLE mode. It is

OFF when the CPU is in STOP mode.
ENabled: This LED is ON when outputs are enabled and OFF when outputs are disabled.

MEMory PROTECT: This LED indicates the status of the memory protect keyswitch. It is ON

when the keyswitch is in the ON position. It is OFF when the keyswitch is in the OFF position.

P1, P2, P3: LED blinks intermittently when there is serial communications on the indicated serial

port (Port 1, Port 2, or Port 3).

Battery Connectors

There are two identical battery connectors. The battery currently installed can remain connected
while a new battery is being installed, minimizing the risk of data loss. A Low Battery Warning
occurs when the battery needs replacement.
When the CPU is in storage, the battery can be disconnected if there is no application program
stored in memory. If a program is st ored in memory, the battery should not be di sconnected, or the
data will be lost.
OK
RUN
EN
MEM PROTECT
P1
P2
P3
Y
R
E
B
A
T
T
Battery
Connectors
Memory
Protect
Keyswitch
LEDs
CPU Mode
Switch
Port 1
RS-232
Port 2
RS-485
Port 3
RS-422/485