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SECTION 2
LOGIC CONVENTIONS AND CIRCUIT DIAGRAMS
2.1
GENERAL DISCUSSION
Quantum's logic diagrams emphasize the functions performed by the logic elements rather than the kinds of
devices used. For example, a NAND gate may appear on a Quantum diagram as either a positive logic AND func-
tion with the output inverted (NAND), or as a negative logic OR function with the inputs inverted (NOR). This prac-
tice runs contrary to some logic drawing standards that require the use of the NAND symbol for both functions, but
aids field service personnel in troubleshooting and system design engineers in understanding the principles of opera-
tion of the design.
This functional approach to logic symbology is basic to the logic documentation conventions employed by
Quantum. The conventions that govern logic symbology, signal nomenclature, and other drawing standards that
may help the reader interpret Quantum logic diagrams, are discussed in the following paragraphs.
2.2
LOGIC SYMBOLOGY
The logic function symbols that Quantum uses in logic diagrams conform closely to those set forth in MIL-
STD-806 or ANSI Y32.14-1973. Small scale integration (SSI) circuits are represented by their function symbol.
Medium scale (MSI) and large scale (LSI) integration devices, such as shift registers, RAMs, ROMs, etc., are
represented by rectangles with function labels. Since both positive and negative logic conventions can appear in a
single diagram, the unfilled-circle negation symbol specified by MIL-STD-806 or ANSI Y32.14-1973 is used to
distinguish between LO true and HI true signals.
Usually, all logic symbols are drawn with inputs on the left and outputs on the right. Some device symbols, such
as flip-flops, show inputs and other external connections on the top and bottom of the symbol for clarity. Also, the
drawings themselves usually show major signal flows from left to right, top to bottom. However, drawing layout
restrictions occasionally require the reverse of this, and that some symbols be drawn with a vertical orientation.
2.3
COMPONENT LOCATIONS
Quantum uses two component location systems. One, shown on the perimeter of the diagram, is useful in
locating a portion of a circuit or a particular component on the diagram itself, and has no other meaning. The other
involves the component identifiers, such as OR gate 4J. The identifier is a "grid coordinate" code for locating that
component on its printed circuit board. Further, a textual reference to a device, such as a flip-flop, will usually fur-
ther identify the device by its major output terminal. In the case of flip-flops, the "Q" output is usually used, i.e. FF
6H-9.
2.4
CIRCUIT DIAGRAMS
The schematic diagrams which follow the integrated circuit illustrations represent the latest version of each cir-
cuit board in current production at the time of preparation of this manual.
There are two important part numbers associated with each circuit board in the Q2080.
I) The PCB Assembly part number identifies the complete circuit board with components installed. This
number is etched onto the top (component) side of the PCBA. The revision letter of the board assembly generally is
marked on this side of the PCBA also.
2) The PCB part number (fabrication number) is the part number of the blank PCB with components. This
number is etched on the bottom (solder) side of the PCB. The revision letter of the fabrication is also etched on this
side.
2-1
REV A
(01/84)
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