Primary and
Standby Unit
System Status
Register
(%SW61)
Schneider Electric recommends that you become familiar with the Hot Standby
status register bit positions.1.
Bits 15 and 16 identify the state of the controller to which your PC is connected.
Reversely, bits 13 and 14 identify the state of the other controller.
For example, with the programming panel connected to the Primary unit, a bit
sequence such as (1,1,1,0) for bits 13 to 16 would normally indicate that this
controller is the Primary unit, and the other controller is the Standby unit. Reversely,
with the programming panel connected to the Standby unit, the same bit sequence
should be (1,0,1,1).2.
These bit indications must match the information displayed on both keypads.
A very important piece of information, given by bit 11, permits you to know if the
current controller is to be considered as the "A-Controller" or the "B-Controller". This
A versus B attribute is selected after identifying the MAC address of the embedded
Ethernet port: A-Controller is the controller whose CPU module shows the smaller
MAC address value. Reversely, B-Controller is the controller whose CPU module
shows the greater MAC address value.3.
Unity use the IEC convention for referencing registers so
Bit 13 is %SW61.3
Bit 14 is %SW61.2
Bit 15 is %SW61.1
Bit 16 is %SW61.0
1. A dedicated EFB exists (HSBY_ST), which allows the user to split onto application
boolean variables the state of these bit positions. In turn these bits may easily be
used to animate an Operator Screen on Unity Pro. Anyway, no doubt a user trained
to directly identify these bits will be an efficient one.
2. The fact that the status register holds potentially different contents on Primary and
Standby proves that the contents of the status register on the Standby is not updated
with the contents of the Primary’s status register.
3. That means that some provisions should be made, at the application level, in order
to be able to cope with a maintenance operation resulting in a MAC address relative
height inversion.
