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Theory of Operation
3-60
2715 Spectrum Analyzer Service Manual
The Power up reset circuit consists of a TL7705 Power Supervisor IC. This IC
monitors the +5 V supply and generates a reset signal on power up. The
capacitor, C101, is used to delay the rising edge of BDRST_L for about 50 ms.
This ensures that if the +5 V supply falls below 4.5 V, the BDRST_L signal will
remain low for a minimum of 50 ms, and that the LCA will go through a valid
reset cycle and reprogram correctly.
Microprocessor
The Microprocessor board is the central processing section of the instrument. It
is used to control all instrument functions including frequency control, imple-
mentation of the human interface, and external port communication through the
GPIB or RS--232C board. The Microprocessor contains the following circuit
blocks (Figure 3--24):
H Microprocessor (CPU)
H Clock Generator
H Interrupt Controller
H Input/Output (I/O) Subsystem Interface
H Memory (RAM and ROM)
H Software Option Jumpers
H Programmable Interval Timer
H Counter System (Figure 3--25)