General - Philips PM2521 Service Manual

6
Fig.
1.
Basic built-up
of
PM2521
CONTROL SECTION DISPLAY SECTION
1.2.2.
Control Section
The
control
section
comprises the following
circuit elements:
—
The
interrupt controller
The
inputs for the interrupt controller are the
mode
switches
and
the trigger
level circuit
output
(timer part)
—
The counter with
its
input control
The
inputs for the counter
circuit are;
—
The
ADC
output
—
The
trigger
level circuit
output (counter
part)
The
input
control
is
directed
from
the microcomputer
—
The
ROM
with address/data decoding
—
The microcomputer 8035
—
The
function selector with decoding
—
The
mode
switches
—
The
relay/FET switch control
1.2.3.
Display section
The display section
consists of:
—
The
display interface
circuit
—
The
5-digit liquid-crystal display
1.3.
FUNCTIONAL DESCRIPTION
1.3.1.
General
in
common
with
most microcomputer-based
measuring
instruments, the Automatic Multimeter
PM2521
is
designed around the microcomputer
integrated circuit
-
an 8035 with
a
4K
external
ROM. The 8035
comprises
a microprocessor with an
internal
64-byte RAM, one
true 8-bit bidirectional port and two
quasi-bidirectional
ports.
In
conjunction with the
4K ROM,
the
pP
controls the timing and measuring
functions of the instrument.
It
also provides the reading of the display.
In the
analog
section,
all
the inputs
are
converted
into d.c. signals, attenuated
as
necessary under pP
control
and supplied to the ADC.
The
ADC
converts these
d.c.
analog representations
of the input signals
into digital logic signals suitable for the
pP.
The
measuring sequence from
analog section to control and
display sections
is
briefly outlined
in
the flow-
chart, Fig.
3.
Fig. 2.
Biockdiagram
PM2521