HP 5004A, Operating And Service Manual

Page: 48 / 74

Model
Service
EXAMPLE 1 says that Z is not true if A is true and B is true or that Z i s true if A and B are not
both true. or This i s frequently referred to as NAND (for NOT AND).
EXAMPLE 2 says i s true if A i s not true or if is not true. Z =A +B. Note that this truth table
i s identical to that of Example 1. The logic equation is merely a De Morgan's
transformation of the equations in Example 1. The symbols are equivalent.
EXAMPLE 3 Z
=
A
+
B or Z
=
A
+
B and,
EXAMPLE 4 Z
=
A also share common truth table and are equivalent transformations of
each other. The NOT OR form (Example 3) is frequently referred to as NOR.
NOTE
In this manual the logic negation symbol is NOT used.
8-17. Logic Implementation and Polarity Indication
8-18. Devices that can perform the basic logic functions, AND and OR, are called gates. Any
device that can perform one of these functions can also be used to perform the other if the re-
lationship of the input and output voltage levels to the logic variables
and is redefined
suitably.
8-19. I n describing the operation of electronic logic devices, the symbol H i s used to represent
a "high level," which i s a voltage within the more-positive (less-negative) of the two ranges of
voltages used to represent the binary variables.
L is used to represent a level," which is a
voltage within the less-positive (more-negative) range.
8-20. A function table for a device shows (implicity all the combinations of input
conditions and the resulting output conditions.
8-21.
I n
graphic inputs or outputs that are active when at the high level are shown
without polarity indication. The polarity indicator symbol that the active (one) state
of an input or output with respect to the symbol to which it is attached is the low level.
NOTE
The polarity indicator symbol is used in this manual.
EXAMPLE 5
Assume two devices having the following function tables.
DEVICE DEVICE
FUNCTION TABLE FUNCTION TABLE
POSITIVE LOGIC
assigning the relationships L=O at both input and output, Device can perform the
AND function and Device can perform the OR function. Such a consistent assignment is
referred to as positive logic. The corresponding logic symbols would be:
DEVICE DEVICE