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

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346 MUSICAL ApPLICATIONS OF MICROPROCESSORS<br />

10 pF<br />

X<br />

AXIS<br />

INPUT<br />

MSB<br />

LSB<br />

Iou!<br />

1408<br />

10 kil<br />

10 kG<br />

TYPE<br />

4016 T= 0.0027,uF<br />

SWITCH<br />

X<br />

OUTPUT<br />

ANALOG + 15 V -15V<br />

SWITCH<br />

ORIVE<br />

10 pF<br />

y<br />

2.5 kil GAIN<br />

TYPE<br />

4016<br />

SWITCH<br />

Y<br />

AXIS<br />

INPUT<br />

MSB<br />

lout<br />

1408<br />

10 kil<br />

10 kil<br />

y<br />

OUTPUT<br />

LSB<br />

+15 V -15 V<br />

(B)<br />

Fig. 11-2 (Cont.). (8) Analog portion.<br />

is simply editing curves or text where the system is waltlng on the user<br />

virtually 100% <strong>of</strong> the time anyway. For other applications, it would be nice if<br />

the display automatically refreshed itself from the display list. One possibility<br />

is to utilize a small microcomputer similar to the music keyboard<br />

driver described in Chapter 9 as a dedicated display processor. The main<br />

system would transfer display list data to it through a serial or parallel port.<br />

Alternatively, in a bus-organized system with DMA capability, the display<br />

processor could interpret a display list area <strong>of</strong> memory shared with the main<br />

system processor. A display program in the dedicated micro would continuously<br />

interpret the list and keep the display refreshed. Using a 6502<br />

microprocessor for the display processor is advantageous because the addressing<br />

modes and overall high speed <strong>of</strong> the 6502 allow complex list structures to<br />

be processed as fast as the display generator can accept data. A 1K or 2K byte<br />

EPROM (2708 or 2716) is plenty large enough to hold the display<br />

interpreter and fundamental list-editing s<strong>of</strong>tware. One to four 2K byte static<br />

RAM chips (6116 type) can easily hold display lists larger than the display's<br />

ability to refresh them at a reasonable rate. A 6522 parallel 1/0 chip provides

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