Detailed Circuit Description; Measuring Sequence - Philips PM2521 Service Manual

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1.4.
DETAILED CIRCUIT DESCRIPTION
1.4.1.
Measuring sequence
After
POWER
ON, the
PM2521
carries
out
some
routines to measure and evaluate the input signals applied.
The
software applications are briefly indicated
by the following sequence.
/
After
POWER
ON,
the
microprocessor
fills
the
RAM
locations
in
the jJP
with conditions
for
jumps
to subroutines.
During the
program these
RAM
locations can be changed by the
program
and manually by
the user (e.g.
UP/DOWN
ranging, +/- buttons,
etc.).
The PM2521
performs
some
internal calibration
routines and
also
checks the analog inputs for
adjust routines (Port 2 of /tP).
This routine prepares the
PM2521
for
a
measurement.
It
reads the function switch setting
and
sets the
required relays,
FET's and
signal lines.
The measurement routine accepts the input
signals,
supplies
the
signals
to the
ADC,
counter and
juP,
and compares with
internal calibration
measurements,
as
required.
In this phase, the data of a
measurement
is
calculated
ready
for
sending to the display
(e.g.
dB
calculations).
This routine despatches the data to the
display.
The
data
may
be a measuring result or
a
message
(e.g.
CAL; OL).
5T3359
81
1130
Fig. 19.
Measuring sequence