Tektronix CSA 803C, Service Manual

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System Functional Overview
Theoryof Operation
3Ć4
After the user requests an operation (with a front panel control for instance),
the Executive Processor (EXP) directs the CSA 803C to perform this operaĆ
tion. Another primary function of the EXP is to execute diagnostic SelfĆTests
on the instrument when poweringĆon or at the user's request. To control
operations, the EXP controls andmonitors the other circuit boards sharing
the executive system bus. Through the executive bus boards, the EXP also
indirectly controls all other instrument boards. The EXP generates comĆ
mands andstatus signals to control onĆboarddevices andI/O devices, such
as GPIB andRSĆ232ĆC interfaces, that help process data andhelp control
the rest of the instrument.
The memory management unit (MMU) arbitrates requests for access to the
Waveform Memory from the following three sources:
the EXP
the Time Base/Controller
the display system
This arbitration allows all three systems transparent access to the Waveform
Memory.
Waveform Memory is sharedamong the following processors:
the EXP
the Display
the Time Base/Controller
While the main function of the Waveform Memory is the storage of waveform
data andwaveform relatedinformation, the sharedmemory is also usedto
pass messages between the Executive, Display, andTime Base/Controller
processors. Eventually, all acquiredwaveforms are transferredfrom the
Acquisition system memory to the Waveform Memory for display.
Executive Processor
Block
MemoryManagement
Unit Block
Waveform Memory
Block