Tektronix TDS 360 Technical Reference

Theory of Operation
3–14
TDS 340A, TDS 360 & TDS 380 Technical Reference
Pots, FPP, and Calibrator. The front-panel processor monitors the front-panel
controls. It consists of a single-chip microprocessor (U101) with built-in RAM,
ROM, A-to-D converter (for digitizing the potentiometer wiper voltages), a
programmable timer (for generating the output of the probe compensator signal),
and a serial communications interface (for data transfer to and from the CPU).
The knob scanner, working with the A-to-D converter internal to the front-panel
processor, produces digital values for the wiper voltages of the front-panel
knobs. Analog multiplexers U420 and U421 select one of 12 possible pot inputs
to read. Although there are only six knobs on the front panel, three are continu-
ous-rotation potentiometers made up of two wipers, separated by 180 degrees,
which contact a single resistive arc.
Three control lines to multiplexers U420 and U421 select the pot input or wiper
voltage to be read. The analog voltage at the wiper of the pot selected is applied
to the front-panel processor. This voltage is digitized, and the amount and
direction of change from the previously stored value is calculated. The change
information is sent to the CPU.
The front-panel processor generates CALSIG. The high level is ≈5 V and the low
level is at ground.
Switches. The front-panel switches and menu switches are arranged in an array of
eight rows and columns. When a switch closes, one row line connects to one
column line through an isolation diode. A complete scan of the front-panel
switches consists of setting all eight row lines low, in sequence, and performing
an eight-column scan to check for a change from the state stored in the front-pan-
el processor. Low bits in the column-line data tell the front-panel processor that a
switch is closed.
LEDs and Power Supply. The LEDs are arranged in groups of eight. They are
connected between the outputs of 8-bit LED latch (U202). When the CPU needs
to turn a particular LED on or off, it sends a command to the front-panel
processor indicating what to do to the LED, and which one to change. The
front-panel processor converts the LED identification number to the LED
address within the latch.
A20 Low Voltage Power Supply
The A20 Low Voltage Power Supply is a switching power converter. It supplies
power to all the circuitry in the oscilloscope.
The Low Voltage Power Supply does not have a main power switch. The
ON/STBY switch, located on the front panel, controls all the power to the
oscilloscope except the standby circuits in the Low Voltage Power Supply.

Tektronix TDS 360 Specifications

General

Brand	Tektronix
Model	TDS 360
Category	Test Equipment
Language	English