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Model
5315A/
8
Service
8-40. The microcomputer
controls
the operation
of the MRC via
the
Address/Command
bus.
Address
lines RG0 and RGl
select one of four
internal
registers, us ing
binary
addresses.
NS0,
NS1,
and NS2
are
nibble
se lect lines, which address
data (nibble
=
four bits
)
withi
n
the
var
iou
s
registers. CS
is
the
chi
p select line,
which
allows
or
disallows
the chip to
respond to
add resses.
IRQ (interrupt
request)
signals
the microcom
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
comma
nd
;s
va lid.
0-42.
The Data/Strobe bus
conta ins
~he
four-b
it
bidirect
ional
data lines,
00-03,
and
the
command line STR which
effects
the
transfer
of measurement
data between
the microcomputer,
the
M
RC
and the display
assembly.
8-43. The
Exponent/A
nnunciator bus
controls the
operation
of the
Gate, Hz, s, "-",
and
decima
l
point annunciators. The four-line
binary
address
on
lines
a,
b,
c,
and d
select
the ex-
ponent
displayed.
CEl
enables
the
display.
8-44.
The multiple register
counter (MRC) is an
L
SI
bipolar
Ie,
utilizing both EFl and
12L
ci
r-
cu
itry.
It
is a
programmable universal
counter
on
a
chip. The reference oscillator
drives
the MRC,
via 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
amplifier
assembl
y
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
-shot
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 nected
to it ;short gate times
with
Rl
and
C19
and
longer gate time when C2 is
added.
5ROS is
the
sample -rate-one-shot
tim-
ing
node.
One of
two
sample rates is selected;
a
short
minimal
samp
le
rate, determined by the
time
consta
nt
of
R8and C18,
or infinite
in Hold,
via 52.
With
SROS
low
(Hold
),
the measurement
will
be made
and
displayed, but no more measurements
will
be made until
the
li
ne
goes
high
.
8-45.
Within the MRC
are four addressable
registers.
The Events
and
Time registers are
counting registers, which are
read
only.
The Status register monitors the
operation
of
the MRC
and
the
Contro
l
register receives
the commands from the
microcomputer and determines the
configuration.
8-46.
The
internal reference oscillator
is
comprised of
a
crystal
controlled
osci llator stage
and
an output
buffer
stage.
Transistor
02
and
crystal
Yl,
along with
associated
circuitry,
form
the
10
MHz oscillator. Capacitor C15
provides regenerative feedback,
wh
il
e
trimmer
capacitors C12
and C14
provide for
fine
and
coarse
frequency adjustments. The
oscillator
10
MHz is
fed
through
buffer amplifier
01
to the
INT
/EXT osci llator switch
53. In
the
INT
pos ition,
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
BNC
(J6). With 53
in EXT,
an external
reference
signal
of
10
MHz,
app
li
ed
to J6,
is
routed
through protection circuitry
CR4, CR5, C5, C6,
and R3,to the
MRC
replacing the
inte
rnal
reference. CR4
and
CRSlimit the
amplitude,
R31imits
the
current,
and C5
and
C6
block dc
com-
ponents.
If
Option
002 TCXO is installed,
10 MHz is routed
through
53 (in
EXT)
to
the MRC
and
output
to
the rear
panel 18.
6-47. The power
supply
provides three regulated and one
un
regu lated
dc
voltage.
The
AC line
voltage
e nters through]1,
through power transformer T1 to
rect
ifi
er
assembly
CR7.
Selection of
line
vo
ltage
is accomplished
th
rough
54 on
531SA models and through the printed circuit card
within
power module
A6
for
53158 models.
CR7 provides
unregulated
+9 and
-9
volts, which is
then
fi ltered
by C25
and C29. CR6
is
a
decoupling
diode for
Option
002.
Switch 51
-1
applies the
unregu lated
+9V dc to
the +5 volt
regulator,
made
upof 03,
04,
Q5,
U3, and
associated circuitry.
6-7
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