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Theory of Operation
3-66
2715 Spectrum Analyzer Service Manual
Allowances have been made for on board programming of the EPROM devices.
On board programming is done by removing J528 (and/or W528) and then
supplying the appropriate timing and voltage signals to program the EPROMs
through connector J550.
There are two jumpers (1 kΩ resistors) on the I/O Subsystem Status Register that
can be used by the CPU to set various software options. These jumpers select the
options shown in Table 3--17.
When SW0 is set to 1 (+5 V), all the debug messages will be printed on the
screen. This greatly increases the amount of time needed to complete the power
up sequences.
Table 3- 17: Definition of Software Jumpers
Jumper Status Definition
SW0 = 0 Do not print debug messages
SW0 = 1 Print debug messages
SW1 = 0 Old Counter Amplifier
SW1 = 1 New Counter Amplifier
The programmable interval timer (U580) is an NEC PD71054 (Intel 82C54). It
contains three programmable timers that are used for various functions by the
CPU. The signal GATE_0, from the I/O Subsystem Control Register, is used to
enable (GATE_0 = 1) or disable (GATE_0 = 0) timers zero and one. The signal
AUDEN is used to enable (AUDEN = 1) or disable (AUDEN = 0) timer two.
The signal CLK88 (7.3728 MHz) is fed into timer one. The output of timer 1 is
then fed into timers zero and two. The output of timer zero is then fed into IR0
of the Interrupt Controller. The output of timer two goes to the Log Board to
generate the audio tones.
For programming details, see the NEC PD71054 or Intel 82C54 data sheets.
The Frequency Counter System consists of buffer amplifiers and three counters.
The three counters are an event counter (28 bits long), the reference/period
counter (29 bits long), and the IF counter (24 bits long).
The event counter consists of devices U290, U480, and counter zero in U470.
The event counter is fed from one of three ports: CFC, DETVID, or OPTION.
These inputs range in frequency from 1 Hz to 40 MHz. The input is selected by
writing the appropriate bits in the Frequency Control Register.
Software Option Jumpers
Programmable Interval
Timer
Frequency Counter
System