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5.
3.7.
2.
3.6
On
return
from
standby, the
standby
IRQ
latch
is
again
set.
This provides
a
microprocessor
interrupt
and
sets the
standby
IRQ
flag as before.
The
positive
-going
output
from IC30d-ll
clocks the
standby
latch
back
to
the reset state, so that the
STANDBY LED
is
turned
off
and
the
power
supplies are restored.
The
microprocessor
resets
the
standby
IRQ
latch
at
the
end
of
the interrupt
routine.
5.3.7.
2.4
The
IRQ
Circuits
5.3.7
.2.
4.1
The
KEYBOARD
DATA READY
line at
PL2
pin
4
goes
to logic
1
when
the
keyboard encoder
has data
available.
This clocks
IC26a
to
the
set state to
provide a
keyboard
IRQ
flag at
IC23-11 and an
interrupt signal
at
IC28b-9,
Interrupts
from
the
measurement system
(MCC
IRQ) and
the
GPIB
interface
(GPIBIRQ)
are
connected
to
IC28b-12 and IC28b-10,
13.
5. 3. 7. 2.
4.2
If
any
of these interrupts occur,
IC28b-8 and IC3Qb-6
will
go
to logic
1.
Provided the standby
latch
IC26b
is
not
set,
IC30b-5
will
be
at logic
1
and
the
interrupt
signal
passes via
IC30a and IC32a
to
IC19-2.
5.
3.
7.
2.4.3
When
the
instrument
is
switched
into or
out
of the
standby
state, the
standby
IRQ
latch IC30c, d
is
set.
The standby
IRQ from
IC30c-10
is
fed to ICl
9-2 via
IC30a and IC32a.
5.3.7 .2.4.4
The
circuit
comprising
R220,
C121,
IC32b,
and
D28
disables
the
microprocessor
interrupt input and
holds
the
GPIB
microprocessor reset
line
low
(via
Q29c), while the
+5V
power
supply
to
R220
is
switched
off.
On
return
from
standby,
Cl
21
charges
and IC32b-4
goes
to logic
0.
The
microprocessor
interrupt
input
is
enabled
and
the
GPIB
microprocessor
is
reset.
The
delay
in
enabling
the interrupts
prevents
the
standby IRQ,
which
occurs on return
from
standby,
from
being acted
upon
before the
power
supplies
are
fully
restored.
5.3.8
Power
Supply Block
5.3.8
.1
Functional Description
5.
3.8
.1.1
A
simplified
diagram
of the
power
supply block
is
given
in
Figure
5.10.
The
AC
supply enters
at
a plug
mounted on
the rear panel and
passes via a fuse
and RFI
filter,
mounted
on
the
motherboard,
to
the
line
switch.
5. 3.8. 1.2
The
switched
supply
is
connected
to the
primary winding
of the
power
transformer
via
the operating- voltage range
selector.
The
voltage
range
selector
is
a
small
plug-in
printed
circuit
board which
is
positioned according to the desired
line
voltage.
5.
3.8. 1.3
The
transformer
has a
tapped secondary winding which
supplies
two
bridge
rectifiers.
The smoothed
but unregulated
outputs
from
the
rectifiers
feed
regulators
providing +11. 2V, -11.2V,
+5V,
+5V
and -5.2V.
The
-5.2V
regulator
and one
of the
+5V
regulators,
which
supply
most
of the instrument's
circuits,
are shut
down
by a
signal
from
the
microprocessor
when
the instrument
is
switched
to
standby.
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