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Analog Input Interface
GLOSSARY
This glossary provides a narrow definition of a term used in this manual. These should not be
regarded as technically complete definitions.
ADC, A -to-D card - see analog-to-digital converter
address data - commands the card receives when the computer reads data from specific address offsets
on the card. These commands specify the gain and channel the card will use to take a reading. See
analog read.
alias - Two signals of different frequencies are aliases of one another if they cannot be distinguished
from each other based on an analysis of samples taken at equally spaced intervals.
analog-to-digital converter - The integrated circuit
(Ie)
which compares the differential input volt-
age on a channel to a reference voltage. The AOC reports what portion of the reference voltage the
input was. A-to-O card refers to the main printed circuit assembly of the HP 98640A.
Analog read - a word-wide (16 bit) read of the A -to-O card where the address used includes an even
offset of between 64 and 126 (decimal), inclusive. The A-to-O will retain the offset (less the unused
Isb) and treat it as an encoded command if the busy bit was not set to one at the time of the read.
busy bit - 16th bit
(01
5) of data returned when an Analog read of the card is made. If this bit is set
to one the remainder of data should be regarded as invalid. Further more, the address data will not be
retained by the card. This bit provides immediate information about the status of the card.
card --Refers to the main printed circuit assembly of the HP 98640A.
center voltage - The voltage half -way between the voltages on the input leads of a channel.
common mode overrange - An error condition due to:
a. One or both input voltages on a channel exceed input voltage limits.
b. A center voltage so close to one of the input-voltage limits that when the signal is
amplified a linear result would be a higher voltage than the amplifier can deliver.
current loop - Refers to a communications or control system which alters current in a circuit to
transmit data or commands. Typically, such systems are referred to by the maximum current the sys-
tem can produce such as "20ma current-loop".
dog bolts - The captive thumbscrews used to secure cover plates to the back of the computer.
't
floating source - A voltage source which is not referenced to ground. A battery is an example.
K, k - Upper-case K stands for 1024 (2 to the 10th power). Lower-case k stands for 1000 (10 to the
3rd power).
Isb - least significant bit
msb - most significant bit
G-I
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