Maintenance Aids; Introduction; Physical Description (Logic); Use Of Relative Level Indicators - Control Data Corporation BR8 SERIES Hardware Maintenance Manual

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MAINTENANCE AIDS
7.1 INTRODUCTION
This section contains detailed information on the logic circuits used in the FDD. The
logic consists of two types of circuits: discrete component and integrated circuits (IC).
Integrated circuits are contained within a single chip and discrete component circuits
contain individually identifiable resistors, capacitors, transistors, etc.
7.2 PHYSICAL DESCRIPTION (Logic)
All components are mounted on one side of the printed circuit board. The board is
8 x 11 inches (203. 2mm x 279. 4mm) and contain both IC and discrete component circuits.
7.3 USE OF RELATIVE LEVEL INDICATORS
The relative level indicator is a small triangle located on the input or output to a
logic block. The presence or absence of this indicator indicates the conditions that
are necessary to satisfy the function of the logic block. The presence of the tri-
angle indicates a 0 logic level on that line is needed to satisfy the function. The
absence of the triangle indicates a logical 1 is needed to satisfy the function.
The relative level indicator depicts the occurrence of inversion. Figure 7-1 shows
some representative examples of the relative level indicator being used in this
manner.
NON-INVERTING
INVERTING
Figure 7-1. I nversion Conventions
7.4 INTEGRATED CIRCUITS
Figure 7-2 shows an example of a schematic block and the information that it contains.
The first line gives the function symbol which identifies the logic function that the block
performs. Refer to Figure 7-3 for a summary of function symbols. The second line
gives the CDC element number. The third line on the schematic block gives the cir-
cuit reference designation.
77834769-A
7-1
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