Kurzweil K2000R - Section 5; K2000 Audio;Power Board Theory; Scanner Microprocessor Theory

SECTION 5
AIJDPWRl.DOC 12/22/92
5.1
5.1.1.1
K2000 AUDIO/POWER BOARD THEORY
SCHEMATIC PAGE 1
SCANNER MICROPROCESSOR
Note: ~er to B10a Diagram (Figure
5.1.6.1 on page 15 ~or assistance.
The M37450 integrated microcomputer (U30, E-3 to E-6) on page 1 of the Audio/Power Board schemat-
ics contains 16K of ROM, 384 bytes of RAM, 8 AID input lines, 2 D/A output lines and 6 ports of
I/O. It is responsible for scanning the keyboard, panel buttons and performance controls. It
also controls the panel LEDs, LCD contrast, and variable-gain amplifiers and audio routing
switches. It communicates bi-directionally with the Engine microprocessor over a 31.25Kbaud se-
rial link.
The M37450 is RESET by the same Signal as the Engine Board and the Effects Processor which en-
ables simultaneous starting. The 10MHz clock for the M37450 is delivered from the Engine via J7
(A-5) .
The analog I/O section will address 8 analog inputs and two analog outputs. It contains only one
8-bit A/D converter and internal circuitry to select which of the 8 inputs is addressed at any
given time. There are two separate latched 8-bit D/A converters. There are separate reference
VOltages for the AID and D/A converters. These are connected to +5Vref. The M37450's digital
circuitry is connected +5Vdig.
It is important to note that during power-up the +5Vref rises faster than +5Vdig which can cause
the M37450 to "latch up" and overheat. D2 (D-6) prevents this by keeping +5Vref from being more
than 0.6 volts more positive than +5Vdig during power-up.
5.1.1.2 MUSIC KEYBOARD INTERFACE
The music keyboard has two PC boards with the keyswitches on them and a cable from each. Each
board has an 8 column by 8 row keyswitch matrix which covers 32 keys with two switches per key.
Connected together, the matrix is 8 columns by 16 rows. Because there are 61 keys on the key-
board, only 58 of the 64 positions on the treble circuit board are connected.
The matrix, part of which is diagrammed below, is connected such that the 8 columns are driven by
Port 2 and the 16 rows are sensed by Ports 0 and 1. During operation, the column being driven is
low and the remaining 7 columns are high. Pull-up resistors in RP7 and RP8 hold all of the rows
high. If a switch contact is closed, it will pull the row to which it is connected low.
Keyswitch isolation is accomplished by the diodes in series with each key contact. The M37450
drives each column in sequence, then reads the rows on Ports 0 and 1. This scan sequence is
repeated every 250uS and the resulting keyboard image (status) is stored in internal RAM. The
high scanning speed is necessary to resolve minute variations in keyboard velocity for expres-
sion.
RIll ,
c.-(;z
ROW JI
(2-C;2
COl. COL COl
~{G. C"fA '114~
. . . .
COL COL
F.v GI ••
...
I ••
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Figure 5.1.1.1 - Portion of keyswitch matrix
Because the keyboard is large, the printed circuit wiring is extensive, and the boards do not
have a groundplane, there is potential for the keyboard to radiate RFI form the constant scan-
ning. R-C filters are used on all keyboard lines to "soften" the waveform edges and suppress RFI
from the clocks. Resistor networks RP1-RP6 are 100 ohm series resistors and 24 individual 100pf
capacitors are used on the scanning lines.
5.1.1.3 DEBUG PORT
J3 (1-5 to 1-6), which is the connector for the bass portion of the music keyboard, is a 26-pin
header, although only a 16-pin header is installed for normal operation. With a 26-pin header
installed, it and J2 (1-3 to 1-4) become a debug port. When JP1 (E-7) is open-circuited (a thin
trace on the solder side must be cut), the M37450 begins operation in "microprocessor mode" in
which case Ports 0 and 1 become an address bus and Port 2 becomes a data bus. The extra 10 pins
on J3 carry the remaining signals needed, including power, to interface to a "debug pod" which
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