Symmetricom TM7000, Руководство пользователя

Страница: 84 / 174

CHAPTER FOUR
THEORY OF OPERATION
4.0
LOGIC DESCRIPTION AND USE
The TM7000 TymMachine TCG/T is depicted by several drawings. One of these drawings is the
Top Assembly drawing A-TM7000 which shows the physical location of the assemblies that are
contained in this instrument. This print should be used to locate connectors on the rear panel and
for quick reference to the physical location of any of the assemblies and controls.
Schematics are comprised of sheets, with each individual sheet number referenced in the lower
right-hand corner of the title block. Each term on a schematic sheet will have a name and may or
may not have a number in brackets [ ] preceding or following it. This number in brackets [ ] (i.e.
the term reference number) indicates the sheet number where that term originates. Example: [2]
OSCLK. This says that the term “OSCLK” shown on Sheet 3 actually originates on Sheet 2. If
the origin of the term is on the same sheet as the term, it won’t have any brackets. This provides
a convenient means of getting back and forth from various pages of the schematic.
Each time a term reference number appears, it will refer you back to the source of that signal. In
each of the schematics there will be a number such as U4, U8, U11 etc. These numbers refer to
the physical location on this assembly for that particular integrated-circuit element. In order to
determine a physical location of an integrated circuit, one would merely refer to the Top
Assembly drawing. On this drawing, each assembly contained within the Basic instrument is
identified by referencing the mechanical view of the top of the instrument. Look for the printed
circuit board of interest. Examine the board until the desired integrated circuit or component is
located.
All references in this discussion will be based on the sheet numbers located in the Title Blocks of
the schematics. The reader should be familiar with the above before proceeding.
4.1 GENERAL
The TymMachine is both a Time Generator and a Time Translator. A Time Generator is a device
which takes a reference frequency and divides it so as to accumulate or “count” time intervals. A
Time Translator is a device which requires a Serial Coded input and “decodes” or “translates”
this input to some other form, usually parallel time data.
In order to better understand the logic organization of the TymMachine, lets first review the
basic configuration of typical timing units.
Symmetricom, Inc. TM7000 TymMachine TCG/T (Rev D) 4-1