Front Panel Controls
(0
and0)
2212
Service Manual
Digital Circuitry
The front panel is the operator's interface
for
controlling
the
user selectable
oscilloscope functions. Along
with
the crt,
it
provides visual feedback to the
user about the present operating state of the instrument.
The front panel micro controller U1401
and
the
main processor
on
the storage
board communicate using a three wire interface;
Clock signal (FP
_CLCK)
Data
input
(into the front panel) line (FP
_SDI)
Data output line
(FP
_SDO)
The 68HC05P7 micro controller has a synchronous serial in-
and
output port
(SIOP), therefore communication needs a minimum software overhead.
The clock signal is supplied by the 68070
main
processor on the processor
board (A15), with a maximum
of
500 kHz, so micro controller U1401 is operated
in
slave mode. fo eight clock pulses one byte is transferred to and from the front
panel micro controller. Every two milli seconds the
main
processor polls the
communication channel. This means that within 2ms U1401 must be ready to
put
data into the SIOP. Therefore
in
the
main
program of U1401 tasks are split
up
in
parts. Between each part a synchronisation byte is
send
so there is always
communication between the processors.
Front Panel Switches
The front-panel switches S1400 to S1465 (38pcs) are arranged
in
a seven-row
by
eight-column matrix (see diagram 14).
When scanning, micro controller U1401 sequentially sets each row line
in
the
LO
state via U1402. When a switch is closed,
it
pulls
down
a column line,
which will be read
by
the micro controller. The intersection of the selected row
and the pulled down column uniquely identifies the switch that is closed.
Since switches S1400, S1401
and
S1402 are
not
momentary switches they are
isolated from the column lines
by
diodes CR1400 to CR1411.
Front Panel Potentiometers
The position
of
the wipers of the seven Front-Panel potentiometers R1410
through R1415B are digitized
by
the 10-bit
aid
converter U1401, which has a
serial interface with the micro controller. Beside these potentiometers also the
CH1
and
CH
2 probe coding circuits (diagram
1)
and
the
plus
and minus peak
detectors (diagram 4) are read. Hold-off potentiometer R1416 is not digitized,
but is directly connected to the circuits involved.
3-
31
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