Eight-Input Priority Encoder 1820-0657 - HP 5340A Operating And Service Manual

Model 5340A
Theory of Operation

4-57. Eight-input Priority Encoder 1820-0657

4-58. Figure 4-26 shows the logic diagram, and outline drawing, for the 1820-0657. This IC
accepts eight active low inputs and produces a binary weighted output corresponding to the
highest order input. Priorities are assigned to each active low input so that when two or more
inputs are simultaneously active, the input with the highest priority appears at the output.-Input
7 has the highest priority. An active low enable input
provided to expand priority encoding to more inputs. "&is mode of operation is acheived by
connecting the- more significant encoder's enable output
enable-input (El). In addition, a group signal is provided which is active if any input is active
and E l is low. As a n example of encoder operation, assume that input 2 and 6 are low and E l is
low. In this case, the encoder gives priority to the 6 input and gives a binary output of AO=H,
Figure 4-26. Eight-Input Priority Encoder 1820-0657
P I N N A M E S
0
El
EO
A2
N O T E S
a 1 U n i t L o a d IU
10 U L
4-18
NUMBERS
'IN
Priority (Active
Priority (Actlve
L O W )
Enable (Active
Enable (Active L O W )
Group Select (Active
Address (Active
L 40 P A H I G H / l 6 L O W
L O W d r i v e f a c t o r a n d 2 0 U
,
I I ,
(El)
and active low enable output (EO) are
(EO)
to the next less significant encoder
13
= P i n
GND =Pin 8
Input
L O W )
Input
Output
Output
L
H I G H d r i v e fact08
3 4
16