Model
5315A
/ 8
Service
8-40. The microcomputer controls
the
operation of
the
MRC
via
t
he
Address/Command bus.
Address lines
RG0
and RGl select
one
of four internal registers,
us
in
g binary addresses.
NS
0,
NS
1,
and
NS
2 are nibble
se
lect lines, w
hi
ch address data (nibble = four bits) within the various
registers.
CS
is
the c
hi
p select
lin
e, which allows
or
disallows the ch
ip
to respond to addresses.
I
RQ
(interrupt request) signals the
mi
crocom
puter when
the
MRC requires service (Le.,
when
a
measurement
is
complete
).
8-41. Command line RIW (read/ write)
con
trols
the
direction of data transfer
on
the
bidirection
Data/ Strobe bus.
Command
line
STR
;s
the
strobe
li
ne, which indicates
an
address
or
command
;s
va
lid.
0-
42.
The Data/Strobe bus conta
in
s
~he
four-b
it
bidirectional data lines,
00-03
, and the
command
line
STR
which effects
the
transfer of measurement data
between
the microcomputer,
t
he
M
RC
and the display assembl
y.
8-43. The Ex
ponent
/Annunciator bus controls the
ope
ration of
the
Gate, Hz, s,
"-",
and
decimal point annunciato
rs.
The four-line binary address
on
lines a, b, c, and d sel
ect
the
ex-
ponent
disp
la
yed.
CE
l enables
the
displa
y.
8-44. The multiple register
counter
(MRC) is
an
L
SI
bipolar I
e,
utilizing
both
EFl
and
12L
ci
r-
cu itr
y.
It
is
a programmable universal
counter
on
a chip. The reference oscillator drives
the
MRC,
v
ia
pin
21.
Inputs from
the
Channe
l A and B amplifier assembly are fed
in
at pins
30
and
28.
An
External
Arm
line, also from the input amplifi
er
assembly is
connected
at pin
17.
In
addition to
the Address/Command and Data/Strobe buses from
the
microcomputer, two
other
contro
l
lines,GTOS an
SROS
are routed
in
to pins 6 and
7.
GTOS
is
the
gate-time-one-s
hot
timing node.
The gate time operates over
one
of two ranges, as set
by
function switch
51
-5
. The
gate;s
deter
-
mined by the time constant of resistor Rl, and the capacitor(s)
con
n
ected
to
it
;short gate times
with
Rl
and C19 and l
onger
gate t
im
e
when
C2
is
added. 5ROS
is
the sample-r
ate
-one-
shot
tim-
in
g node.
One
of two sample rates is selected; a short minimal sample rate,
determined
by
the
time constant of R8and C18,
or
infinite
in
Hold, via
52.
With
SROS
low (Hold),
the
measurement
w
ill
be
made and displa
ye
d, but
no
more measurements w
ill
be
made
until
the
li
ne goes high.
8-45. Within
the
MRC are four addressable registers. The Events and Time registers are
co
unting registers, which are read onl
y.
The Status register monitors
the
operation
of
the
MRC
and
the
Contro
l register receives
the
commands from
the
microcomputer and
determines
the
co
nfiguration.
8-46. The internal refer
ence
oscillator
is
comprised of a crystal
contro
lled osci
ll
ator
stage and
an
output
buffer stage. Transistor
02
and crystal Yl, along with associated circuitry, form
the
10
MHz osc
ill
ator. Capacitor C15 provides regenerative feedback, wh
il
e trimmer capacitors C12
and C14 provide for f
in
e and coarse frequency adjustments. The oscillator 10 MHz
is
fed
thro
ugh
buffer amplifier
01
to
the
INT
/EXT
osci
lla
tor
sw
it
ch
53.
In
the
INT pos
iti
on,
the
internal
10
MHz
sign
al
is
routed
to the MRC (
U2
pin
21
)
via
dc
blocking capacitor C6, and (
5315B
models only)
to the rear panel B
NC
(J6
). With
53
in
EXT,
an external reference signal of 10 MHz, app
li
ed
to
J6,
is
rout
ed
through
protection circuitry
CR4, CR5,
C5,
C6,
and
R3
,to
the
MRC replacing
the
in
ternal
reference.
CR4
and CRSlimit
the
amplitude, R31imits
the
current, and
C5
and
C6
block
dc
com
-
ponents. If
Optio
n
002
TCXO
is
installed, 10 MHz is r
outed
through
53
(in
EXT
)
to
the
MRC and
output
to
the
r
ear
panel
18.
6-47. The power supply provides
three
regulated and
one
unregu
la
ted
dc
voltage. The
AC
line
voltage enters
through]1,
through
power
transformer
T1
to
rect
ifi
er
assembly
CR7.
Selection of
line vo
lt
age
is
accomplished through
54
on
531SA
models and
through
the
printed circuit card
within power module
A6
for 53158 models.
CR7
provides unregulated +9 and
-9
volts, w
hi
ch is
t
hen
fi
lt
ered
by
C25
and
C29.
CR6
is
a decoupling
diode
for
Opt
ion
002.
Switch
51
-1
app
li
es
the
unregulated +
9V
dc
to the +5 volt regulator,
made
u
pof
03,
04
, Q5,
U3,
and associated circuitry.
6-7
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