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Th e HP Inter face Bus transfers data and commands between th e co mp o ne n ts of an i n st rum e
n
tation syste m on 10
sig n al lines . Th e inte
r
face fun ctions for eac
h
syste m component are
p
er for m ed within t
h
e co mp o nent so o n ly
pass i ve cabling is nee
d
ed to co
nn
ect t h e system . T
h
e cables connect all inst
r
u m ents, co
n
trollers, and ot
h
e r
co mp one
n
ts of t h e syste
m
i n parallel to t h e signal li n es .
E ig h t of t
h
e lines ( D I01- D 108) a
r
e reserved for t h e tra n sfer of data a nd ot h e
r
messages i n α byte-se r ial, bit- p a r alle l
ηιαητι e
r
. Data and message t
r
a
n
s
f
e
r
is asynchronous, coo r di n ated by t he t h ree h a n ds h a
k
e li n es (D A
V
, NRFD,
N DAC) . T
h
e ot h e
r
five lines are for co n trol of bus activity . Fi g u re ΑΙ
s
h
ows tile li
n
es .
Devices connected to t
h
e bus may
b
e tal
k
ers, listeners, or co n trollers . T h e co
n
tro l le r
d
i ctates t
h
e r u le of eac h of
tile other
d
evices by setti n g t
h
e ΑΤΝ (attent i on)
l
i n e true a nd se nding ta lk or l i ste n a dd
r
esses oil tile data lines
(DI01-D1OS) . Ad
dr
esses a
r
e set i
n
to eac
h d
evice at t h e ti m e of syste
m
con fig
u
ratio n
e
i t h e
r b
y switc
h
es built into
the device ιιί by junipers oil α Ρ('
b
oard . W h ile t h e ΑΤΝ l i ne
i
s t rue, all devices must l i ste
n
to t h e
d
ata lines . Wh en
t
h
e Α " Ι Ν li
n
e is false, only
d
evices t
h
at have bee n a dd ressed will actively send o
r
receive data . All ot
h
ers ig n o
r
e
t h e data lines .
Several listeners can be active simultaneously b u t only one tal k er call be active at α t i me . Wh e neve r α tal
k
add r ess
is pu t Oil the data lines (w h ile ΑΤΝ is tr u e), all ot he r tal
k
e
r
s will
b
e a u to m atically ιι naddressed .
Information is trans m itted oil t
h
e data li n es u nder sequential co n t rol of t h e t
h
ree h a n ds h a
k
e lines . No ste p in t
h
e
se
q
u e
n
ce ca
n b
e i n itiated un til the previous ste p is comp leted . Information transfe r can proceed as f ast as devices
can res p o
n
d, b u t no faster t h a n allowed
b
y (lie sl owest dev i ce
p
rese n tly a d dressed as active . Th is
p
e
rm
its se ve r al
devi ces to rece i ve t
h
e same message byte concurrently .
T
h
e ΑΤΝ li
n
e is one of' the five co n trol lines . Wh en ΑΤΝ is true, addresses a nd universal comm a n ds are
tra n s
m
itted on only se v en o f the data li n es using t he ASCI I code' . W} ι e η ΑΤΝ is false, any code of 8 bits or less
ιι n d erst υ od by both talke
r
and listener(s) may be
u
sed .
1l ι e et
h
er co n t
r
ol lines are Ι F Γ , REN, S
R
Q, ΕΟΙ .
A
PPEN
DIX Ι
THE HP I
N
T
ERF
AC
E BU
S
I F C Onte
r
face clea
r
) places tile inte
r
face system in α
k
now n
q
ui escent state .
A ppe n d ix Ι - Th e HP Inte rf ace Bu s
M
ode l 59313 Α
R
ΈΝ (
r
e ιιιο te ena
b
le) is u sed w i t
h
ot
h
er coded
m
essages to select e i t
h
er local or r e
m
ote co n tro l
o
f eac h dev i ce .
Any active device call set th e S
R
Q (serv i ce re
q
u est) line tr u e .
T h
is in d icates to t
h
e contr olle
r
t
h at so
m
e device oil
the
b
u s wants atte n tion, say α co u nte r
t
h at
h
as
j
u st com p leted α tim e- in terva l m easu re m ent a
n
d wants to t r a n smi t
tile r eading to α pr inter .
ΕΟΙ (end or identify) is
u
sed
b
y α device ( ο i n dicate t h e e nd of α
m
ult ip le-
b
yte t r a n s fe r seq u ence . Wh e n α
co ntrolle
r
sets bot
h
tile ΑΤΝ a nd ΕΟΙ lines tr u e, eac h device cap able of α
p
arallel poll in d i cates
i
ts c ur rent statu s
on tile D IO line assigned to it .
In t h e i n terest of cost-e ffectiveness it is
n
ot necessa r y for every device to be ca p a
b
l e o f responding to all t h e
l
i n es .
Each can b e desig n e d to r es p ond only to th ose lines that are
p
e r tin ent to
i
ts function on the
b
u s .
Th e operation o f th e inte
r
face is ge n erally controlled
b
y o ne dev ice eq u ipp ed to act as co n t
r
o l le
r
. I t u ses α
g
r o up
o
f co mm a nds to direct tile ot h e r
i
n st r u m ents on t h e b u s i n car
r
yi ng out t h e i
r
fu nctio n s o f talking a n d liste n i ng .
* Ame
r
ica n Standard Code fo
r
Information
I
nterc
h
ange .
Α - Ι - 1
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