Front Panel
The front panel circuits (schematic shown on page 9-16) consist of
vacuum fluorescent display control, display high voltage drivers, and
keyboard scanning. Communication between the front panel and
floating logic circuits is accomplished through a 4-wire bidirectional
serial interface. The main
CPU
,
U500
, can cause a hardware reset to
processor
U600
by signal
IGFPRES
. The front panel logic operates from
+13 volts (logic 0) and +18 volts (logic 1). The four serial communication
signals are level shifted by comparator
U602
from the floating logic 0 V
to 5 V levels to the 13 V to 18 V levels present on the front panel
assembly. The front panel logic low supply (+13 volts) is produced by the
+18 volt supply and 4.7 V zener
CR606
. Level shift outputs for the front
panel receive data are clamped to the 13 volt supply
VLB
.
Display anode and grid voltages are +18 volts for an “on” segment and
–18 volts for an “off” segment. The –12 V cathode bias for the display is
provided by filament winding center tap bias circuit
CR556
,
R556
, and
C559
on the power supply schematic (see page 9-15). Keyboard scanning
is accomplished through a conventional scanned row-column key matrix.
Keys are scanned by outputing data to shift register
U601
to poll each
key column for a key press. Row read-back data are parallel loaded into
shift register
U601
and shifted back into processor
U600
for decoding and
communication to the floating logic circuits.
5
Chapter 5 Theory of Operation
Front Panel
107
Summary of Contents for 34401A
Page 1: ...Keysight 34401A 6 Digit Multimeter Service Guide ...
Page 2: ......
Page 17: ...Contents 10 ...
Page 18: ...1 Specifications 1 ...
Page 33: ...26 ...
Page 34: ...2 Quick Start 2 ...
Page 54: ...3 Menu Tutorial 3 ...
Page 65: ...58 ...
Page 66: ...4 Calibration Procedures 4 ...
Page 98: ...5 Theory of Operation 5 ...
Page 115: ...108 ...
Page 116: ...6 Service 6 ...
Page 132: ...7 Replaceable Parts 7 ...
Page 143: ...136 ...
Page 144: ...8 Backdating 8 ...
Page 149: ...9 Schematics 9 ...