Alesis QS7.1 Manuel de service télécharger pdf (Page 22)

Alesis QS Series Keyboards Service Manual V1.00 11/19/06

➫ DD0-DD7 Data Buss bits 0 to 7. Correspond to the upper 8 data bits of

the H8.

➫ A0 H8 Address Buss bit 0

➫ RD H8 ReaD enable

➫ WR H8 WRite enable

➫ KEY Chip select line from GAL (Mapped I/O)

➫ KEYINT Output to H8 interrupt line

➫ KEYCLK Clock input from H8

➫ ROW0-7 Row input from keyboard switch matrix

➫ COL0-21 Column input from keyboard switch matrix

➫ VSS1-4 Source Supply (GND)

➫ VDD1-4 Drain Supply (+5V)

2.34A Reading Velocity

Velocity response is measured through the time differential between two switch closures

and works like this:

➠ The harder a key is pressed, the

faster it moves.

➠ Since Rate = Distance/Time

knowing the time it takes to move

the key through a specific distance

tells us how fast it’s moving and

thus the force acting on it.

➠ This is accomplished by using 2

switch contacts mounted at

different distances from each other.

The rubber in the keypad acts as a

spring, both absorbing the

compression of switch 1, as well as

pushing the carbon contacts away

from the PCB contact points when

the key is release.

➠ The Keyscan ASIC counts up the

time it takes between switch 1

closing and switch 2 closing. Since

distance (between the switches) is

preset in the design, time difference

is taken as a direct measure of

velocity.

2.34B QS8 Key Construction

All keyboards in the QS Series function

identically in an electrical sense. However, since the QS8 keyboard is different in mechanical

construction from the rest of the line, a word or two about it is appropriate at this point. In order

the simulate the action of a true piano keyboard the FATAR TP/20 keyboard uses moving

metal weights striking a felt strip to emulate the action of the piano’s hammer striking a string.

Figure 5 shows the basic setup of the keys. Note the “action” of the two “levers” involved

in the process. The first lever which is the key itself is single ended, with it’s fulcrum located at

the “back” end of the key. The second lever is the double ended counterweight. With it’s

Figure 4 - Keyboard Velocity Reponse

1 2 ... 17 18 19 20 21 22 23 24 25 26 27 ... 96 97

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Alesis QS7.1 Manuel de service Page 22

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