Philips PM 3266 - Page 117

122
If
the
instrument
is
busy
with
a particular
cycle,
e.g. the erase
cycle,
then
a new
pushbutton
combination
cannot
interrupt
this
cycle.
This
provision
is
achieved
by
the fact
that
the D
flip-flop
D2204
only
loads
the
new
pushbutton
combination
of
it
receives
a
clock
pulse
on input
pin 9.
This clock
pulse
(7
Hz)
is
derived
from
an
oscillator
formed
by
D2203/8,
9,
10
and
D2203/12,
13,
11.
The
oscillator
is
switched
on
if
pin
9 of
D2203
is
at logic
1. A logic
1 is
produced
from
the
BUSY signal
(busy notj
during
a cycle,
via
diode
V2221,
and
via R2203
and
V2219
if
the
MEMORY
OFF
function
is
selected
(diodes
V2217,
V221
8
non-conducting
by
logic
1's on
D2202
outputs
12
and
15).
DUAL
OSCILLATOR
The
dual
oscillator
formed
by
operational
amplifiers
D2222
and
D2221
produces
two
different
square-wave
output
signals,
both
with
a
frequency
of 100
Hz.
The
output
signal
present
on
pin
7 of
D2221 has
a duty
cycle that
is
adjustable
between
0 and
30 %.
This
signal
is used
as
the variable
persistence
pulse
and
in the WRITE
mode it
is applied
to the
amplifier
that
drives
the front
mesh
of
the
c.r.t.
The output
signal
on
pin 8 of D2221
has
a duty
cycle that is
adjustable
between
0 and
80 %.
This signal
is
applied
in the
STORE
mode
to the
amplifier that
drives
the flood
gun
accelerator
electrode
of the
c.r.t.
On output
pin
6 of
D2222 a
triangular
signal
of
approximately
100 Hz
is available.
Because
of the RC
feed-
back
loop
this
operational
amplifier
functions
as
a
100
Hz
master
oscillator. This
triangular
output
waveform
is
applied
to the
positive
input
(pin
5)
of D2221.
Via
the PERSISTENCE
control R16
and operational
amplifier
D2221
12,
3,
1
a variable
d.c.
level is
applied
to the negative
input (pin
6)
of D2221 . In
this way,
the duty
cycle
at the output
(pin
7)
of
D2221 is
adjustable
between
0 and
30 % by means
of R16.
The 100
Hz
triangular
waveform from
the
master oscillator
D2222
is also applied
to the
positive input (pin
10)
of D2221. Via
the INTENS
control
R14
and operational amplifier
D2221/12,
13,
14
a
variable
d.c. voltage is
applied to the
negative
input (pin
9)
of D2221.
In this way, the
duty cycle
on output pin 8
of D2221 is
adjustable
between
0 and
80 % by means of
R14.
This is operative
in the STORE
mode.
TIMER
In the
WRITE and FAST
modes,
pulses need to be applied
to
the
various electrodes
of the c.r.t.
at
specific
intervals and
in the correct
sequence after
the ERASE
pushbutton has been operated.
The timer,
comprising
five
delay units
connected
in cascade, provides delay times of 1
00 ms, 500
ms, 300 ms, 300 ms and 300
ms.
On the
outputs
of inverters D2212,
timing
pulses are produced after 100
ms (pin
6),
600 ms (pin
4),
900 ms
(pin
2),
1 200
ms (pin
10)
and 1
500 ms (pin 1
2).
The timer is triggered
at
the
moment that the depressed
ERASE pushbutton
is released, this moment being
referred to
as t^.
At the time t^ a positive-going
clock pulse
reaches the clock input (pin
3)
of
D
flip-flop
D2208. This enables the flip-flop to come into
the
SET
condition if
the data
input (pin
5)
is high.
In the WRITE
and FAST modes,
this data
is made high via D2207/1,
2,
3.
In the SET condition
of
D2208 flip-flop the Q output (pin
1)
is high
and therefore the
input of the first timer
section
becomes high.
This timer consists of R221
1,
V2206,
buffer
D2213/14, 1
5
and
C2208.
At
the
time that the timer input
becomes high,
input
14
and output
1
5 of D2213 are low.
Capacitor C2208
now charges via R221
1 ;
diode
V2206
is not conductive.
After a time of
100
ms C2208 is charged sufficiently for input 14 of D2213 to detect
a high level and output
1
5
of
the timer
also becomes high.
This high output
is passed
to
the
input of the next timer section (the 500 ms timer) which consists of R2222,
V2207, D2213/1
1,
12
and
C2209
and
operates in the same way as
the
100 ms timer section.
The
succeeding
timers have identical
networks, the difference
in delay times being achieved by different values of the resistors
that
charge
the capacitors.
These timing pulses
are gated
to
give
the following output
waveforms:
Output Gate
Logic
Level
Duration after
tg
D2211/10
high 100 ms
D2211/11
high
600 ms
D2214/11
high in WRITE
mode
low in
FAST mode
900 ms
D2211/4
high
1200
ms
D2211/3
low
in WRITE
mode
high in
FAST
mode
1500
ms