CHAPTER
3
PRINCIPLES
OF OPERATIO
N
3-1.
IN
TRO
D
~
CTION
T
hi
s c
h
apter
descI
j
bes
t
h
e
b
as
i
c f
un
c
t
io
nal
operation
of
t
he iSBC 655 System
Ch
assis.
Mos
t
of the in-
fo
r
mation
in this 0rapter
ce
nt
e
r
s a
rou
n
d
the opertion
of
th
e f
r
ont panel
,
Discuss
ion
of t
h
e powe
r
s
uppl
y
i
s
cov
e
red
in a seprrate
p
ubli
c
ati
o
n,
t
he
iSBC 6
3
5
Power Suppl
y
Ha
r
dware
R
e
fe
re
nc
e M
anual
,
Order
N
umb
er
9800298.
Th
e
chassi
s
functi9nal
com
p
o
n
e
n
ts
i
n
c
lud
e
the front
pa
n
e
l
with
s
witche
$
an
d
i
n
d
ic
a
to
rs,
t
wo
cooling fan
s
,
po
w
e
r
supply
,
fo~r s
l
o
t
ca
rd
c
a
ge
/
ba
ck
plane,
and a
do
m
estic
(l15
v
It)
powe
r
cord
.
T
he
follo
w
in
g
pa
ra
graphs
descri
e t
h
e
ma
j
o
r
co
mp
o
nent
s
of the
ch
a
ssis.
I
3-3.
FR
ONT P
A
l
NEL SWITCHES AND
IND
ICATq
RS
Th
re
e
switches
reside on t
h
e i
SBC 65
5
front
panel:
the
p
ower
ON
/
OFF
i
ndi
ca
tor
/
swi
t
ch,
the
RUN
sw
itch
, and the HALT switc
h.
I
The
po
wer ON
/
OFf
indica
to
r
/
sw
it
c
h
(S
I)
is
located
on
the l
ef
t
side of tHe fro
n
t
panel
.
Wh
e
n power i
s
ap-
plie
d
,
the indicator
w
i
l
l
il
lumin
at
e.
Th
e
illuminator
bu
lb
is accessed
by pu
ll
i
n
g
of
f t
h
e
t
r
an
s
luc
e
nt
s
witch
ca
p.
The
o
t
h
er
two froIl
j
t
p
a
n
e
l
sw
it
c
he
s
ar
e
momentary
roc
ker
ty
p
e
s
, labeled
R
ESE
T
(S3) and INTERRUPT
(S4
). Th
e RESET
~
witc
h
is w
ir
e
d
t
o
p
in 14 of the
bac
kplan
e.
When d(
j
presse
d,
the
s
witch
g
enerates
the
R
E
SET
/
signal, which is sy
non
y
mou
s
wi
th IN IT
/
on
the
b
ack
pl
ane.
The
(
li
p-
fl
o
p
which a
c
tu
a
lly
generates
R
E
SET
/
is located
d
m
the f
ront pan
e
l pr
i
nted
circuit
boa
rd (P
CB), and is show
n
i
n
f
igu
r
e 4-5.
Th
e
INTE
RRUPT s
~
it
c
h fun
c
tions in a
s
imilar man-
n
er
.
Wh
e
n
the swi
t
f
h
is
d
e
pressed
,
cir
c
uitry on the
fr
o
nt pan
el PCB gener
a
te
s the INTl
/
si
g
nal
,
which is
wi
red
to
pi
n 42 of
tHe
b
ac
kplane
(
refer t
o
figure 4-2).
Th
e
RUN
and
H
AL
T
in
di
c
ator
s
ar
e
l
ig
ht emitting
dio
de
s
mou
nted
on
t
h
e
f
ront
pan
e
l PCB
.
The RUN
a
n
d
HA
L
T
indicatdrs
illuminate
a
s
a function
of
t
h
re
e
s
ta
t
u
s signals: ~
A
I
T
/
,
HALT
/
,
a
n
d ALE
.
The
RUN
indic
ator
illu~i
n
a
te
s
when
the CPU
is exe-
c
u
t
ing an
instruction
.
The
i
ndi
c
ator
will be off when
the CPU is in the WAIT state or a H
ALT
instruction
has been executed.
The HALT
indicator
illumina
t
e
s
after the CPU
ha
s
executed
a HALT
instruction.
A fro
nt pa
n
el RESET
or an INTERRUPT
will remo
v
e
t
he
H
ALT
s
tate
.
Notice
that
when
the CPU
i
s
in
t
h
e WA
I
T
state
neither
the RUN
nor the HALT
in
dicato
r
s
are on
.
The illuminator
circuitry
i
s s
ho
w
n in
figure
4
-5.
3
-
4:
LIN
E
V
O
LTA
G
E S
E
LECT SWITCH
AND LINE FUSE
The line voltage select switch is
a
dj
acent
t
o
the card
-
cage fan, and is shown
s
chemati
c
all
y
in f
i
gure 4-2.
The switch
has two positions,
corr
espo
ndi
ng
to the
two usable line
v
oltages;
115 V
A
C
and 23
0
VAC. A
ke
y
ed switch locking
plate
s
ecure
s
th
e switch in one
position.
The switch can be set to the
ot
h
e
r
position,
onl
y
by loosening
the two plate
hol
d-down
screw
s
,
and flipping
the plate over
.
Each
s
id
e of t
h
e plate is
labeled
.
Fuse F 1 is located
on the rear cha
ssis
p
an
el
,
right
s
ide. A 2
.
5 ampere
fu
s
e
s
hould
be u
sed for 230 volt
operation
and a 5 ampere
fuse i
s
u
sed fo
r 1
15 volt
operation.
The line filter is located
directly
b
e
lo
w the fuse
.
The
line filter hardware
also function
s
a
s the
po
wer cord
connector.
The chassis
uti
l
izes
two fans for coolin
g
pur
poses
.
Both are located
on the power ON
/
O
FF
switch side
of the chassis.
Air flow is directed
in
to t
he
chassis,
with one fan cooling
the power suppl
y an
d th
e other
cooling
the cardcage.
Power
for each
fan
i
s derived
directly from the line voltage
.
3
~.
~
BCW4CARDCAGE
AND
BACKPLANE
The cardcage
houses
a total
of four
i
S
BC bo
ards
.
Considered
part of t
h
e cardcage,
the b
ac
kplan
e
is a
printed
circuit
b
oard
with Multibu
s
and oth
er
con
-
nectors
attached
.
Operating
voltage
s
r
ea
c
h
th
e
boards
via t
h
e backp
l
a
n
e
and
all inte
r
board
co
m-
munication
occurs on the M
u
lti
b
us.
