8.3.3 Clamp Diode Structure

The inputs and outputs to this device have both positive and negative clamping diodes as depicted in Figure 8-1.

CAUTION

Voltages beyond the values specified in the Section 6.1 table can cause damage to the device.

The recommended input and output voltage ratings may be exceeded if the input and output clamp-

current ratings are observed.

GND

Logic

Input

Output

VCC

Device

-IIK

+IIK

+IOK

-IOK

Figure 8-1. Electrical Placement of Clamping Diodes for Each Input and Output

8.4 Device Functional Modes

Table 8-1. Function Table

INPUTS

OUTPUT

A

B

C

D

Y

H

H

H

H

H

L

X

X

X

L

X

L

X

X

L

X

X

L

X

L

X

X

X

L

L

SN74HC21, SN54HC21

SCLS087F – DECEMBER 1982 – REVISED JUNE 2021

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