of Microprocessors

288 MUSICAL ApPLICATIONS OF MICROPROCESSORS
Direct Digital Interface
The interface between digital signals from the computer and control
inputs of the signal-processing components can often be simplified. The
reason is that standard voltage levels and response functions are not needed,
since all control paths are local to the module. Thus, a current output DAC
might feed directly into a current-controlled oscillator without conversion to
standard voltage levels, exponential conversion, etc. A multiplying DAC
could be used to directly control gain without transconductance gain cells
and so forth. The result is that a voice module will cost considerably less than
+5V
PROCESSOR
aus
a
a
PORT
I
TYPICAL
BUS DRIVER
a
UPPER
ADDRESS
TO
TTL
LOGIC
IN
MODULE
PORT
2
aus
DRIVERS
LOWER
ADDRESS
a
PORT
3
BUS
DRIVERS
PORT
4
BUS
DRIVERS
a
LOWER
DATA
SETTLE
DELAY
STROBE
WIDTH
SINGLE-SHOTS
ADDRESS
AND
>------------- DATA
VALID
STRoaE
Fig. 8-8. Voice modular synthesizer digital bus