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 generatesa reset signal on power up. The
capacitor,C 101, is used to delaythe rising edge of BDRST_L for about 50 ms.
This ensures that if the +5 V supply fallsbelow 4.5 V, the BDRST_L signal will
remain low for a minimum of 50 ms, and thatthe LCA will go through a valid
reset cycle and reprogram correctly.
Microprocessor
The Microprocessor boardis the central processing section of the instrument. It
is used to control all instrument functionsincluding frequency control, imple-
mentation of the human interface, and ext ernal port communication through the
GPIB or RS--232C board. The Microprocessorcontains the following circuit
blocks (Figure 3-- 24):
HMicroprocessor (CPU)
HClock Generator
HInterrupt Controller
HInput/Output (I/O) Subsystem Interface
HMemory (RAM and ROM)
HSoftware Option Jumpers
HProgrammable Interval Timer
HCounter System (Figure 3--25)