Theory Of Operation; General; Pro-One General Block Diagram - Sequential Pro One Technical Manual

SECTlON
2
THEORY OF OPERATION
2-0 INTRODUCTION
This section explains t h e Pro-One's
hardware
theory
of
operation. The microcomputer
program (software) is not generally discussed
because
i t is proprietary
and
because the
program details
are
usually not-relevant to s e r v i c e problems. That is, you c a n l t
"fixt'
t h e s o f t w a r e (you
-
can replace it,
by
replacing t h e Microcomputer IC). Note t h a t if you
f i r s t understand t h e hardware surrounding
t h e
microcomputer, you will
be able
to
deduce
t h e basic program
f u n c t i o n s .
2-1
GENERAL
1
The Operation Manual CMlOOB c o v e r e d general function
and
signal flow of t h e voice
and modulation sections. The Pro-One is a monophonic synthesizer in which the
analog
voltage-controlled sound sources and modifiers
are
controlled by a microcomputerized
keyboard, a s shown in Figure 2-0.
Figure
2-0
PRO-ONE GENERAL BLOCK
DIAGRAM
r
-
KYUU L V
AUOlQ
The microcomputer generates the keyboard control voltage (KYBD CV), which is t h e
main determinant of oscillator pitch, and t h e GATE and TRIGGER (TRIG) signals,
which controi t h e f i l t e r and amplifier envelope generators.
KEYW&D
Figure 2-1
shows
m o r e functional detail. The integrated microcomputer contains a
central processor unit CCPU), read-only memory (ROM3, and random-access
memory
(RAM).
The CPeJ foliows t h e program i n ROM by which it
f'reads"
t h e keyboard,
SEQUENCER, ARPEGGIATE, and MODE switches
and
forms t h e appropriate output
signals, The
CPU uses
RAM
t o
keep track
of
the
keyboard and switch status and t o
store latched arpeggios and sequences.
To play a
note
t h e microcomputer f i r s t
reads
t h e keyboard ta find out what key
is
pressed, t h e n sends t h e key'number in parallel, 6-bit binary form to t h e digital-to-
analog converter (DAC). When it receives t h e DAC
ENbBLE (EN) signal,
the DAC
converts
t h e key
number to
the
analog KYBD CV for
OSC
I'A,
OSC, 8, and
t h e
FILTER.
T h e Microcomputer
then
issues the- TRIG and
GATE
s i g n a h which enable t h e Filter and
Amplifier Envelope Generators. The TRIG only appears briefly when t h e key is first
struck. When t h e key Is released,
t h e
GATE goes
off,
initiating t h e RELEASE period(s1.
h .
,
DATA
9
For
t h e
remainder of this section, please refer t o Figure 2-2, Abstract Schematic, and
t h e
Interconnect Diagram a n d Schematics {SD 121JSD 112) in Section 3.
MICRO
GATE
COMWTER
TRIG