of Microprocessors

608 MUSICAL ApPLICATIONS OF MICROPROCESSORS
TIME PHASES
MINOR CYCLE COUNTER
" ONE MINOR CLOCK CYCLE "'
-INTERNAL -1-EXTERNAL ----
I
01112/ 30 1 1 1 2 13
[JX'-- ....:.. JX,'--.:.;I+~I_
FREQ, AND ACCUM, MEMORY DATA ~ .::=,
ADDER OUTPUT ~ 'c=J:.
CLOCK ADDER HOLD REG, r1L _
ACCUMULATOR MEMORY WRITE 0 rI.. _
XTERNAL ADDRESS --,
~~~~OtM INTERNAL ADDRESS E ""- -'
ADDRESS HIGH 7 BITS
SEL,
{
LOW 7 BITS F .......
4116 ROW ADDRESS STROBE G__-Jl
4116 COLUMN ADDRESS STROBE H ,.;,.
FREQ, CONTROL {EXTERNAL ---,
~f~EOtTY ADDRESS INTERNAL A .. , --'
~Rr!i~ECONTROL MEMORY B ....l
4116 WRITE
DAC HOLD REG. CLOC K
DAC SETTLING
CHANNELfSAMPLE
~~~PUT tHOLD
J i ... ...;;s.
K~
-------~""..~----
Fig. 17-14. Multiplexed oscillator timing diagram
as required by the 4116s, 1 The frequency control memory address must also
pass through a selector to allow the control computer to write frequency
control words into the memory, This may be implemented with a single
74157, The 20-bit adder will use five cascaded type 7483A 4-bit adders,
Unfortunately, there are a few timing and design details that require
additional latches to correct, One problem is that the 7489 memories do not
have an edge-triggered write, This means that a race condition is possible
when writing, which can be corrected by inserting a 20-bit holding register
between the adder output and the accumulator memory input. Another
problem is that the 4116 waveform memory only activates its data output for
a short time at the end of a memory cycle, Thus, another holding register
lThe type 4116 RAM actually time multiplexes 14 address bits on 7 addtess pins. Two
clock inputs called row address strobe (RAS) and column address strobe (CAS) trigger
internal latches, which then reconstruct the full 14-bit address, The reader should
consult the manufacturer's data sheet (Mostek Corporation) for full details,