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SM8000 Series Programming 49
Control Register (cont.)
D7
BBM (Break-
Before-Make) /
MBB (Make-
Before-Break)
Enable Bit
0 = BBM/MBB operation on this plug-in module is disabled
1 = BBM/MBB operation on this plug-in module is enabled
Pon state = 0
If this bit is set, the relays on this module will be sequenced to
effect proper BBM or MBB operation. If this bit is not set, the
plug-in module will process the newly written relay data as
immediate data, writing it directly to the relay driver ports. No
BBM or MBB sequencing will take place.
While this feature is enabled, the initial write to the module will
start the delay timer running and begin the BBM or MBB
operation. Since the relays are controlled by the 16-bit registers,
only the effected 16 relays will perform the BBM/MBB operation.
To overcome this fact, any subsequent writes to the module,
during the initial delay timer time-out period, will be accepted and
processed. In addition, the delay time will be reset and begin
counting down again. Once the delay timer has timed-out (this
indicates that the relays have settled into their BBM/MBB state),
writes to the module will not be accepted and may result in a Bus
Error depending on the value programmed into the delay timer.
This is because the delay timer is reset at the end of the initial
time-out and is used to time the final relay closure into their post
BBM/MBB state. The module Busy signal will only complete
once the final relay closure state is reached.
If this bit is set and no value has been loaded into the Delay
Register, the plug-in module will act as if this enable bit is not set
and load all of the relay drivers with immediate data.
*This bit is unused on the SM8000 and should always be sent to 0.
D6
BBM/MBB Select
Bit
0 = BBM operation on this plug-in module is selected
1 = MBB operation on this plug-in module is selected
Pon state = 0
*This bit is unused on the SM8000 and should always be sent to 0.
D5
Access LED Fail
Bit
0 = non-active
1 = active
Pon state = 0
D4
Relay Reset Enable
Bit
0 = The Openbus signal is not enabled to reset this module's relays
1 = The Openbus signal may be selected to reset this module's
relays
Pon state = 0
Note: Bit D3 must be set to 1 also, to allow the OpenBus signal to
reset this module’s relays