Tektronix 2715 Software Option Jumpers, Programmable Interval Timer, Frequency Counter System

Theory of Operation

3-66 2715 Spectrum Analyzer Service Manual

Allowances have been madefor on board programming of the EPROM devices.

On board programming is done by removingJ528 (and/or W528) and then

supplying the appropriate timing and voltagesignals to program the EPROMs

through connector J550.

There are two jumpers (1 kΩresistors) on the I/O Subsystem Status Register that

can be used by the CPU to set various softwareoptions. These jumpers select the

options shown in Table3 --17.

When SW0 is set to 1 (+5 V), all thedebug messages will be printed on the

screen. This greatly increasesthe amount of time needed to complete the power

up sequences.

Table3 -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 programmabletimers 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) timerszero 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. Theoutput of timer 1 is

then fed into timers zeroand 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 amplifiersand three counters.

The three counters are an eventcounter (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 frequencyfrom 1 Hz to 40 MHz. The input is selected by

writing the appropriate bits in the Frequency Control Register.

Software Option JumpersProgrammable IntervalTimerFrequency CounterSystem