FEB. 21,1980

1	RS FLIP FLOP (2/4 IC3)

(a) PLAY Mode
When the START switch S5 is turned ON, the Q cutput goes to H and trig-
gers the Clock Generator (2). Mhen the STOP switch S6 is turned ON, the
Q output goes to L and the Clock Generator stops oscillation. At   this
time, the Q output goes to H and resets the Binary Counter (5)

(b) WRITE Mode
The Q output goes to H when S5 is turned ON, and goes to L when S6   is
turned ON. This condition is written in the Memory IC1 as a data.

2	CLOCK GENERATOR (2/4 IC3)

The frequency of this oscillator is controlled with TEMPO VR-5.     This
oscillator functions in PLAY mode only, and feeds clock pulses to   the
Counter  (5)	

3	SCHIMITT TRIGGER (Q15, 17, 18)

This circuit functions in WRITE mode only. The collector of Ql5 goes
H when either the START switch S5 or the STOP switch S6 is turned   ON,
and goes to L when the switch set to ON is turned OFF.

4	DELAY CIRCUIT (Q16)

The output from the Schmitt circuit (3) is intergrated, and fed to the
base of Q16. Then the signal is trimmed to square wave at collector of
Ql6. This output signal is differentiated and becomes pulses, and then
is applied to the R/~W terminal of IC1.
The two pulses lag a little behind edges of Scmitt (3) output pulse.

5	DUAL BINARY COUNTER (IC2)

This circuit counts pulses from the clock generator  (2)   in PLAY mode,
and counts pulses from the Schmitt trigger (3) in WRITE mode, and then
outputs binary-coded signals from the terminals Ql-Q5; Ql-Q4 denote  16
steps composing each rhythm. Signal from Q5 is applied to A7 only  when
the VARIATION switch is set to AB.
To the terminal A7, the L level voltage is given when the switch is set
to A and H when switch is set to B.

DR-55

6	256 x 4 BIT CMOS MEMORY (IC1)

Reading/writing from/to this memory is  as  described  below.
The upper 3 bits designate rhythms 1-8, the next one bit designates
VARIATION A and B, and. the lower 4 bits 16 steps in one rhythm.
In PLAY mode,  the terminal CE2 is connected. to the Clock generator
output.  The memory functions only when the clock is H, and outputs
H's or L’s from DO 1-4.
(When the clock is L, DO 1-4 becomes high impedance.)

In WRITE mode, when the terminal R/~W becomes L,a data from the flip
flop is written in one of DI 1-4 via Sl.A previously stored data is
rewritten from  DO  via  R61-R64 to the remaining three DI's.

The Vcc of this rnemory chip is directly connected to  the dry cells
regardless of power switch positions,  since the chip draws only  a
very slight idling current during stand-by.  As a result,  the data
is guaranteed to be stored as long as the dry cells maintain voltage
value higher than  a specified. level.
The capacitor C39 (22 mfd.) connected to the terminal Vcc can substi-
tute for the dry cells by its charge for several minutes when   the
cells are absent during replacement.

7	VOlCE GENERATOR (Ql, 2, 3, 7, 8, 9, 10, ll)

BD, SD and RS are triggered by pulses from the respective DO’s. HI
HAT is triggered by pulses from the counter IC2 or the Clock  gen-
erator IC3 by every step or every other step.

8	ACCENT (Q3)

Each sound source output is mixed and outputted through the resis-
tor network in which Q3 is connected in parallel.When ACCENT pulse
is outputted from DO l,  Q3 turned ON,  and in this ON period  the
signal amplitude increases.  The DO l pulse can be externally out-
putted through the CSQ jack.When this jack is enga.ged, however,the 
ACCENT function of the DR-55 proper becomes invalid.