1-10 Series 90™-70 Enhanced Hot Standby CPU Redundancy User's Guide – May 2000 GFK-1527A
1
Basic CPU Redundancy Setups
There are three basic CPU Redundan cy setups:
Single Bus with Preferred Ma ster
Single Bus with Floating Master
Dual Bus with Floating Master

Single Bus with Prefer red Master: GHS Contro l Strategy

This type of system uses a single Genius bus with bus controllers in each PLC. The Primary Unit
is always chosen as the active unit when the units initially synchronize.
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
SP
S
B
T
M
R
C
M
G
B
C
B
L
O
C
K
Only Critical Data Transferred
B
TM............ Bus Transmitt er Module
GBC............ Genius Bu s Controller
PS.............. Power Sup ply..
CPU........... Central P rocessor Unit.
R
CM........... Redundancy Communications Module
B
LOCK....... Genius I/O Block (or Field Control)
The single bus with preferred master setup is suitable if:
A. The application does not require redundant I/O buses, AND
B. It is desirable to minimize the amount of data transferred between units, OR It is desirable
that the Primary Unit always becomes active at synchronization.
Single Bus with Preferred Master requires selection of the GHS control strategy.
The GBCs must be configured with th e following settings. Note that the G BCs can al so be
configured with Redundant Mode = NONE but RED CTRL provides more diagn ostics and will be
preferred in most installations.
Redundant Mode = RED CTRL
Paired GBC = External
Serial Bus Addr = 31 (Primary Unit) or 30 (Secondary Unit)
Assuming that Redundant Mode is set to RED CTRL, the redundant I/O bloc k s must be
configured with the following settings:
(Hand-Held Monitor) CPU Redundancy = HOT STBY MODE
(Hand-Held Monitor) BSM Present = NO
(Programming T ool) Redundancy = YES