Microcomputer Control - Fluke 76 Service

76
Service
INPUT
VOLTAGE

Microcomputer Control

A microcomputer, integrated within U4, controls the various instrument functions and
drives the display. The position of the rotary switch, S1, is decoded by the
microcomputer from the three inputs F0, F1, and F2. All function modes, input ranging,
signal routing, active filter enable, a/d timing and mode are controlled by the
microcomputer.
2-8
BUFFER
1
+
–
2
3
4
+
VOLTAGE
REFERENCE
SWITCH AUTO INTE- READ
NO. ZERO GRATE +INPUT
1 ON
2 ON
3
4
5 ON
INTEGRATE
RAMP
ZERO
BASELINE
16.7
AUTO ZERO
mS
SAMPLE #1
(1 FULL RESOLUTION CONVERSION)
AS SEEN AT INTEGRATOR OUTPUT
Figure 2-4. A/D Converter
INTEGRATOR
–
+
5
131.072 kHz
READ
HOLD
–INPUT
ON ON
ON
ON
ON ON
READ
HOLD
RAMP
8.33
mS
SAMPLE #2
8 MINOR CONVERSIONS, 200 mS
COMPARATOR
REFER TO WAVEFORM
–
+
COMPARE
A/D
CONTROL
CLOCK
MICROCOMPUTER
REPEAT
SAMPLE #8
l4f.eps
2-14.