Page 191 - Electrical Engineering Dictionary

will be passed through a device if that de-
vice is not requesting service, or not passed
D through if the device is requesting service.
(3) an interrupt-prioritizing scheme in
which the interrupt acknowledge signal from
the CPU is connected in series through all
devices. A shared interrupt-request line con-
d axis See direct axis.
nects all devices to the CPU with a single
common line. When one (or several) devices
D flip-flop a basic sequential logic cir-
activates its request line, the CPU will (af-
cuit, also known as bistable, whose output
ter some delay) respond with an acknowl-
assumes the value (0 or 1) at its D input when
edge to the first device. If this device did re-
the device is clocked. Hence it can be used as
quest an interrupt, it will be serviced by the
a single bit memory device, or a unit delay.
CPU. However, if the device did not request
an interrupt, the acknowledge is just passed
D’Arsenval meter a permanent-magnet
through to the next device in the daisy chain.
moving-coil instrument with a horseshoe
This process is repeated until the acknowl-
form magnet. It measures direct current only.
edge signal has passed through all the con-
nected devices on this chain. The scheme
D-TDMA See dynamic time division
implements prioritized service of interrupts
multiple access.
by the way the devices are electrically con-
nected in the daisy chain: the closer a device
D/A See digital-to-analog converter.
is to the CPU, the higher its priority.
A more general case exists where several
DAC See digital-to-analog converter.
daisy chains are used to form priority groups,
where each chain has a unique priority. The
Dahlin’s method a synthesis procedure
CPU will service interrupts starting with the
for finding a digital control law that will pro-
daisy chain having the highest priority. In
duce a defined closed loop behavior for a
this scheme, any device may be connected to
given process, when it is controlled in a feed-
more than one priority group (chain), using
back configuration. The synthesis equation
the interrupt priority level appropriate for the
is
particular service needed at this moment.
1 − e −T/λ z −N−1
k(z) =
1 − e −T/λ −1 − 1 − e −T/λ z −N−1 DAMA protocol See demand assign
z
multiple access protocol.
1
×
g(z)
damage the failurepattern ofan electronic
where k(z) is the pulse transfer function for or mechanical product.
the synthesized controller, T is the sampling
time of the digital control loop, λ is the time damped sinusoid a sinusoidal signal mul-
constant specified for the closed loop system, tiplied by a decaying. An example is x(t) =
NT is the process deadtime, and g(z) is the 10e −3t cos(10t).
pulse transfer function for the process.
damper winding an uninsulated wind-
daisy chain (1) a type of connection when ing, embedded in the pole shoes of a syn-
devices are connected in series. chronous machine, that includes several cop-
(2) a hardware configuration where a sig- per bars short-circuited by conducting rings
nal passes through several devices. A signal at the ends, used to reduce speed fluctuation

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2000 by CRC Press LLC