Section II. LOGIC CIRCUIT DESCRIPTION

TM 11-6625-444-14-2

Section II. LOGIC CIRCUIT DESCRIPTION

The outputs from A2-U57 are then directed to

5-7. Introduction

the range encoder, A 2 - U 6 7 , an eight-line to

three-line priority encoder. In parallel with these

This section contains detailed circuit descrip-

inputs, are range command signals from the re-

tion of the range, function and dc ratio logic cir-

uits of the voltmeter. It includes logic truth ta-

mote input connector and the auto range de-

bles to aid in locating and isolating a logic mal-

coder, U52. Depending on the "logic state" of

function to a specific integrated circuit. Refer to

A2-U57, pin 9 and 2, either manual, remote or

t h e range and function selection diagrams,

autor ange commands will be selected.

g i v e s timing relationships that are helpful in

understanding the analog-to-digital conversion

process.

The three-line output of range encoder, A2-

U67 is then applied through inverters to another

5-8. Range Logic Tables

decoder, A2-U250. There are really four input

lines to A2-U250 but the "D" input is fixed at

To understand the range logic flow, refer to

ground and thus; is always at a logic "low". This

the Range Selection diagram, figure 5-1 and ta-

bles 5-4, 5-5, and 5-6. Manual inputs are ap-

input logic to A2-U250 then selects one of the

plied through the front panel push buttons to

output lines to be "low". The "low" output line

A2-U57, the manual range decoder. This is a

from this decoder determines which range has

four-line BCD to ten-line decimal decoder.

been selected.

Table 5-4. Manual Range Selection Logic, A2-U57