HP 3438A - Page 62

Section Vlll Model 3438A
8-46. HP-IB 'Theory. The H P-IB is an 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 I
I !
I I
i I
I I I
T '.--T
I I + DCI
I I
I I
FIXED TIME FIXED TIME - -
1 I
-
I
I.6rns -
- tt oomrd
----
I
4 - + - 10ornsl- --4
-
LJ ...,
0 0 0 0 --
0
Figure 8-8. Integrator Output.
RUN-UP
8-47. The 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 to I5 instruments can he interconnected in one HP-IB
system. Figure 8-9 is a pictorial of the lnterface
Connections and Bus Structure.
0 ~ 200mr
!
I
8-48. Eight of the signal lines are termed DATA lines
and are used to carry coded messages. The coded
messages may represent addresses, program data,
measurements, or status bytes. The same DATA lines are
used for input and 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 ill
A VALID f DAVl
NOT READY (NRFDI
NOT DATA ACCEPTED INDAC I
INTERFACE CLEAR
(IFCI
ATTENTION fATN)
SERVICE REOUEST ISROI
REMOTE ENABLE 1 REN )
ENO-OR-IDENTIFYIEOII
8-49, Data is transferred by means of an interlocked
"handshake" technique which permits asynchronous
Figure 8-9. lnterface Connections and Bus
communication or data transfer at the rate of the slowest
Structure.