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Musical-Applications-of-Microprocessors-2ed-Chamberlin-H-1987

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CONTROL SEQUENCE DISPLAY AND EDITING 345<br />

Keeping the I mage Refreshed<br />

To maintain the image on the screen without flicker, the list interpreter<br />

would have to be called at least 40 times/sec. An easy way to keep the<br />

display refreshed and do other work as well is to have an interval timer<br />

interrupt 40 times/sec. The interrupt service routine would refresh the display<br />

once and return. If priority interrupts are available, the display should<br />

probably be the lowest priority. If more than 25 msec is required to display<br />

the list, the system would revert to a state in which the list size determines<br />

the refresh rate, which would be less than 40 Hz.<br />

Obviously, the system can become completely tied up refreshing the<br />

display if the image is complex. Often this is not a problem if the application<br />

PORT I<br />

81TS<br />

0-7<br />

SAVE X<br />

~<br />

..2....-- 0 7475<br />

7475<br />

00 0<br />

00<br />

-.!.....- C OC C OC<br />

L- 8 08 8 08<br />

~A OA A OA<br />

CLKCO<br />

r- CLKCO<br />

>- CLKA8 ~ CLKA8<br />

MOVE X<br />

-!- -0<br />

7475<br />

00 0<br />

7475<br />

.L -C oc C OC<br />

~ -8 08 8 08<br />

.L -A OA A OA<br />

>- CLKCO ~ CLKCO<br />

- CLKA8<br />

L-<br />

CLKA8<br />

00<br />

MOVE Y<br />

7475<br />

..2....-- 0<br />

00<br />

-.L- C<br />

OC<br />

L- 8 08<br />

~A OA<br />

CLKCO<br />

~ CLKA8<br />

r-i- f-O<br />

7475<br />

00<br />

~f-C<br />

OC<br />

6<br />

f-8 08<br />

~<br />

'-'-f-A<br />

OA<br />

~ CLKCO<br />

ENOMATCH<br />

50 )J~'C<br />

~<br />

n CLKA8 +15 v<br />

DRAW--------------1<br />

I<br />

(A)<br />

TO Y<br />

AXIS<br />

OAC<br />

I kil<br />

lout<br />

:>0-4.----0 +15 V= OFF<br />

+IOV 0= ON<br />

470 il<br />

ANALOG<br />

6;>

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