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Alesis QS Series Keyboards Service Manual V1.00
11/19/06
18
Table 2 - Pin to Pin Connections for 25 Pin PC Serial to QS
Purpose
QS Serial Pin
PC Pin
HSKO (Enable 4-12V)
1
5
Return (Enable Return)
2
4
TXD
3
3
GND
4
7
RXD
5
2
NC
6
NC
NC
7
NC
NC
8
NC
Table 3 - Pin to Pin Connections for MAC Serial to QS
Purpose
QS Serial Pin
MAC Pin
1MHz
1
2
NC
2
1
TXD -
3
5
GND
4
4
RXD-
5
3
TXD+
6
8
GPI (NC)
7
7
RXD+
8
6
2.51 QS Serial Input
PC/MAC input is passed through a buffer/translation stage consisting of U2A U31C
U24C and some resistors. R8 and R7 R96 and R97 R85 and R86 provide some resistive
isolation and R8 R96 R82 in combination with R27 R94 R83 provide hysteresis for
waveshaping the incoming signal. R9 and R10 R95 and R93 R83 and R84 act as pullups to
further assist in waveshaping. The output of the comparator is resistively isolated from the H8
input port by R28 R87 R74. Pullup resistor R30 R41 R50 ensure the correct TTL signal levels
(pulled up to +5V).
2.52 QS Serial Output
PC/MAC output initiated by the H8 processor is differentiated into the balanced signals
required by the MAC via the comparator pair of U2D and U2C U31B and U31A U24A and
U24B. (Note that the PC interface ignores the TXD- and RXD- lines.) Pullups R26 and R25
R96 and R81 R73 and R67 help maintain the outgoing signal despite possible losses from
long cable runs. R6 and R24 R85 and R80 R72 and R71 help match impedances as well as
current limit and resistively isolate the signal before output.
2.53 PC/MAC Switch
Note the seemingly minor hardware changes that occur when switching between the PC
and MAC lines. Since these changes are critical this switch should be checked carefully when
computer interface problems occur. The PC version sends and receives a D.C. voltage
handshake signal (Enable). The MAC needs to see a bit clock handshake signal which it uses
to determine BAUD rate.
Содержание QS6
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Страница 24: ...Alesis QS Series Keyboards Service Manual V1 00 11 19 06 15 Figure 5 QS8 Key Construction ...
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