Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 10 Page 72 of 265
4
4
G
G
E
E
N
N
E
E
R
R
I
I
C
C
S
S
P
P
E
E
C
C
I
I
F
F
I
I
C
C
A
A
T
T
I
I
O
O
N
N
S
S
4.1 Controller Operation
In common with the ST800, the ST900 and ST900 ELV Controllers are phase
oriented. Timings and demands are associated with phases and the control
philosophy is designed to give right-of-way to phases in an optimum manner.
It is necessary to group phases into stages for Manual Control, operation in Urban
Traffic Control Schemes and in Cable-less Linking Schemes. The traffic
requirements and safety constraints also condition the grouping of phases into
stages.
The controller receives requests for ROW from the following:
a) ‘On-street’ detection equipment and pedestrian push-buttons
b) The UTC computer
c) The Cable-less Linking Facility (CLF)
d) Manual inputs
e) Special requests, e.g. hurry calls
The controller then orders the appearance of phases in accordance with the
controller strategy, the current mode operative and the demand requests for ROW.
The controller will always change stage cyclically.
4.2 Phases
The ST900 Family supports up to 32 phases. These may be all real phases or a
combination of real and software (known as dummy) phases.
4.3 Stages
The ST900 Family supports up 32 stages (Note: Stage 0 is normally ALL RED)
4.4 Timings
All controller timings are stored in EPROM at configuration time. These timings are
subsequently transferred to battery supported RAM during controller initialisation.
Once in RAM most controller timings can be varied by handset commands. Once the
data has been loaded from EPROM this action cannot be repeated without a
complete controller initialisation using a different EPROM. This prevents the
accidental overwriting of any configuration data that may have been set up using the
handset.
The battery-backed RAM is maintained by both a Lithium primary battery on the
main processor card, and by a ‘Gold-Cap’ capacitor, giving an additional 4-hour
backup to retain RAM data whilst the Lithium battery is being replaced.
Alternatively, the complete controller configuration, including its timings, may be
loaded directly in the controller’s battery supported RAM from a PC. With the PC