Display - Fluke 27 Service Manual

readings) Second, if the Touch-Hold button is momentarily pressed at any time, then the
full-resolution conversion is forced to complete in spite of input or test lead conditions.
The microcomputer also sets the required A/D converter mode. A single mode is used in
all voltage and current conversions, but there are three ohms function A/D converter
modes, a diode test mode, and two power-up test modes (battery test and self test). The
microcomputer sends the proper code to U1 to select the required A/D converter mode.
Following each group of 10 samples, in normal operation, the microcomputer sets the
autozero flag.
Both manual and autoranging are controlled by the microcomputer. The microcomputer
loads a range register in U1 in conjunction with a mode-dependent map. In autorange,
the analog filter is disabled to increase the autoranging speed.
Peripheral components Q13 and C12 force the microcomputer to reset when the function
switch is moved to OFF. A voltage-divider network (R3, R4, and C13) supplies a mid-
level voltage to drive the multiplexed display.

2-10. Display

The liquid crystal display (LCD) operates under direct control of the microcomputer.
Characters are generated by the computer and displayed on the LCD. Both digital
readings and an analog bar-graph display are presented, in conjunction with annunciators
and decimal points. Refer to the Fluke 27 Users Manual for a more detailed description
of the display.
Theory of Operation
Block Diagram Description
2
2-7