4-275
Functional Diagram
Gated Inputs
During normal system operation of a latch, signals on the bus
at the device inputs will become high impedance or make
transitions unrelated to the operation of the latch. These unre-
lated input transitions switch the input circuitry and typically
cause an increase in power dissipation in CMOS devices by
creating a low resistance path between V
CC
and GND when
the signal is at or near the input switching threshold. Addition-
ally, if the driving signal becomes high impedance (“float” con-
dition), it could create an indeterminate logic state at the input
and cause a disruption in device operation.
The Intersil 82C8X Series of bus drivers eliminates these con-
ditions by turning off data inputs when data is latched (STB =
logic zero for the 82C82/83H) and when the device is disabled
(OE = logic one for 82C86H/87H). These gated inputs dis-
connect the input circuitry from the V
CC
and ground power
supply pins by turning off the upper P-channel and lower N-
channel (see Figures 1, 2). No new current flow from V
CC
to
GND occurs during input transitions and invalid logic states
from floating inputs are not transmitted. The next stage is held
to a valid logic level internal to the device.
DC input voltage levels can also cause an increase in ICC if
these input levels approach the minimum V
IH
or maximum
V
IL
conditions. This is due to the operation of the input cir-
cuitry in its linear operating region (partially conducting
state). The 82C8X series gated inputs mean that this condi-
tion will occur only during the time the device is in the trans
parent mode (STB = logic one). ICC remains below the max-
imum ICC standby specification of l0mA during the time
inputs are disabled, thereby, greatly reducing the average
power dissipation of the 82C8X series devices
Typical 82C82 System Example
In a typical 80C86/88 system, the 82C82 is used to latch
multiplexed addresses and the STB input is driven by ALE
(Address Latch Enable) (see Figure 3). The high pulse width
of ALE is approximately 100ns with a bus cycle time of
800ns (80C86/88 at 5MHz). The 82C82 inputs are active
only 12.5% of the bus cycle time. Average power dissipation
related to input transitioning is reduced by this factor also.
DI
O
DI
1
DI
2
DI
3
DI
4
DI
5
DI
6
DI
7
DO
0
DO
1
DO
2
DO
3
DO
4
DO
5
DO
6
DO
7
OE
STB
D Q
CLK
FIGURE 16. 82C82/83H FIGURE 17. 82C86H/87H GATED INPUTS
P
P
P
N
N
N
STB
DATA IN
INTERNAL
DATA
V
CC
V
CC
P
P
N
N
OE
DATA IN
INTERNAL
DATA
V
CC
P
N
V
CC
82C82
