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1-12 Series 90™-70 Enhanced Hot Standby CPU Redundancy User's Guide
–
May 2000 GFK-1527A
1
Dual Bus with Floating Master: GDB Control Strategy
This type of system uses dual buses with bus controllers in each PLC. No switchover occurs on
initial synchronization to make the Primary Unit the Active Unit. Bus Switching Modules (BSMs)
are required in accordance with the traditional configuration of a Dual Bus network. This option
provides redundancy of both the PLC and the I/O bus.
C
P
U
C
P
U
B
T
M
R
C
M
G
B
C
30
Secondary Unit Primary Unit
31
B
L
O
C
K
B
L
O
C
K
P
S
P
S
B
T
M
R
C
M
G
B
C
B
L
O
C
K
Critical Data + Redundant
Outputs Transferred
30
G
B
C
G
B
C
31
Bus Switching Module
The Dual Bus with floating master setup is suitable if:
A.
The application requires redundancy of the PLC and I/O bus, AND
B.
The Active unit should not switch when the Primary Unit is returned to service.
Dual Bus with Floating Master requires selection of the GDB control strategy.
The GBCs must be configured with the following settings
Redundant Mode = DB/RC (Dual Bus/Redundant Controller)
Paired GBC = INT/EXT (Internal External)
Serial Bus Addr = 31 (Primary Unit) or 30 (Secondary Unit)
The I/O blocks must be configured with the following settings:
(Hand-Held Monitor) CPU Redundancy = HOT STBY MODE*
(Hand-Held Monitor) BSM Present = YES
(Hand-Held Monitor) BSM Controller = YES or NO (depending on the block)
(Programming Tool) Redundancy = YES
* Configuration as Duplex mode is also permitted; duplex default also needs to be properly
selected. . (See “Duplex CPU Redundancy” on page 1-13.)