ROLAND DR-55
Service Manual

DR-5 5
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 substitute 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 generator IC3 by every step or every other step. 8 ACCENT (Q3)

Each sound source output is mixed and outputted through the resistor 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 outputted through the CSQ jack.When this jack is enga.ged,