HP 5004A, Operating And Service Manual

Page: 52 / 74

Model
Service
8-30. Control
Blocks
8-31. A class of symbols for complex logic are called control blocks. Control blocks are used
to show where common control signals are applied to a group of functionally separate units.
Examples of types of control blocks follow.
R I G H T
L E F T
Register control block. This symbol i s used with an associated array of flip-flop
symbols to provide a point of placement for common function lines, such as a
common clear.
Shift register control block. These symbols are used with any array of flip-flop
symbols to form a shift register. An active transition at the inputs causes left
or right shifting as indicated.
Counter control block. The symbol is used with an array of flip-flops or other
circuits serving as a binary or decade counter. An active transition at the or
-1
input causes the counter to increment one count upward or downward,
spectively. An active transition at the input causes the counter to increment
one count upward or downward depending on the input
OUTPUT
Selector control block. These symbols are used with an array of OR symbols to
provide a point of placement for selection (S) or gating
(G)
lines. The selection
lines enable the input designated I,
....
n of each OR function by means of a
binary SO is the least-significant digit. If the level of these lines is
low, polarity indicators ( will be used. The gating lines have an AND relation
with the respective input of each OR function: with the inputs numbered
with the input numbered
2, and so forth. If the enabling levels of these lines
i s low, polarity indicators ( will be used.
Output selector control block. This symbol i s used with a block symbol having
multiple outputs to form a decoder. The selection lines enable the output de-
signated
....
n of each block by means of a binary code where
SO is the
significant digit. If the level of these lines i s low, polarity indicators will
be used.