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23
I
b)
Control outputs
i
The microcomputer
controls the analog section,
in
accordance with
the input information
received,
by
I
means
of reed
relays
and
FET
switches.
The
output
data
is
clocked
into
a
relay
control unit
which
supplies
function
and
range information to the analog section
for
switching purposes. Additional outputs
are
set/reset
commands
for
the timing
measurements,
trigger
level,
dB
conversion,
and
ZERO
SET command
i
for
the
relative
reference
value.
/.
3. 5. 5.
R
OM's and
address /da
ta
decoding
The program
memory
for
the microprocessor
is
stored
in
two 2k
ROM
memories.
During
an
instruction cycle,
data
is
fetched
from
the
ROM's
by
the
/tP.
This requires that the
ROM
locations are
first
addressed
whereupon
the
ROM
responds
by
sending the
instruction or data to
the
/xP.
The
addresses
for
the
ROM's
are
decoded from
data
sent
out
on
the
8-bit
databus
lines
and
the high-order
program
lines
from
port 2 of the microprocessor.
These
additional
program
lines
are
used to
extend
the
address capability of the
bus.
The
decoding
is
achieved
by
bistable latches
controlled
by
the
ALE
(address latch enable)
output
of the
/xP.
The
data
output
from
the
ROM's
is
controlled
by
the
PSEN
(program
store enable)
signal
from
the
/xP,
which
is
gated to
give a
chip
select signal
to
either
ROM
depending
on
the
stated
of the
signal
line
P23.
1.3.6.
Display section
\
The
display section of the
PM2521
contains three
LCD
(Liquid Crystal Display) interface integrated
circuits
'
that
accept
serially
clocked
output
data
from
the
^xP
to drive
the
display.
I
/
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