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Section Vlll
Model 3438A
8-46. HP-IB 'Theory. T h e
H
P-IB is a n instrumentation
interface which simplifies the integration ofinstruments,
calculators, and computers in a system.
AUTO ZERO
NOTE
HP-IB is Hewlerr-Packard's implementation
IEEE Std. 488-1975, "Standard Digital
Interface for Programmable Instrumenta-
1
ion".
1
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I
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I
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I
I
I
I
T
' . - - T
I
I
+
DCI
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I
I
FIXED TIME
FIXED T I M E
- -
1
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-
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-
-
tt
o
o
m
r
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I
4
-
+
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-
LJ
. . . ,
0
0
0
0
- -
0
Figure 8-8. Integrator Output.
RUN-UP
8-47. T h e
H
P-IB employs a bus of 16 active signal lines
grouped into three sets:
( I )
Data
HCCD
(2) Data Byte Transfer Control
(3) General lnterface Management
RUN-DOWN
AUTO ZERO
Up t o
I5
instruments can he interconnected
in
one HP-IB
system. Figure 8-9 is a pictorial of the lnterface
Connections and Bus Structure.
0
~
2 0 0 m r
!
I
8-48. Eight of the signal lines are termed D A T A lines
a n d are used to carry coded messages. T h e coded
messages may represent addresses, program data,
measurements, o r status bytes. The same D A T A lines are
used for input a n d output of messages in a bit-parallel,
byte-serial form. Normally, a seven-bit ASCII code is
used with the eighth bit available for Parity Checking.
I
I
i
l
l
A VALID f D A V l
NOT READY ( N R F D I
NOT DATA ACCEPTED I N D A C I
INTERFACE C L E A R ( I F C I
A T T E N T I O N f A T N )
SERVICE REOUEST I S R O I
REMOTE E N A B L E
1
REN )
E N O - O R - I D E N T I F Y I E O I I
8-49, D a t a is transferred by means of a n interlocked
"handshake" technique which permits asynchronous
Figure 8-9. lnterface Connections
and
Bus
communication o r data transfer a t the rate of the slowest
Structure.
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