About The Pro-One Basic Operation Front Panel Back Panel Routine Maintenance Service

Section 5: Service

5—6 Digital Interface

Use of the digital interface for external computer control requires both some simple hardware modifications to the Pro-One and the creation of software for your system. If you doubt your technical ability to install the interface, please see an SCI Authorized Service Center or contact our Service Department. However please note that we must leave all questions of programming your system to you.

  1. Remove U113 (see Figure 5-1) 8021 microcomputer from its socket. Keep it safe. Note that with the 8021 removed, the Pro-One's keyboard cannot operate.
  2. Jumper pin 2 of the 8021's socket to J101-7. Pads are provided on the printed circuit board (PCB) for this purpose.
  3. Add R 1182, 10K-ohm, ¼W, 5% resistor where shown on Figure 5-1.
  4. Table 5-0 lists pin assignments. Mate J101 with a 14-wire ribbon cable terminated in a DIP plug. (There are six spare lines).
  5. Table 5-0

    DIGITAL INTERFACE PINS (J101)

    1

    D5

    2

    D4

    3

    D3

    4

    D2

    5

    D1

    6

    D0

    7

    GATE

    8

    -DAC EN

    9-14

    GROUND

    The interface is compatible with standard TTL logic, where a 0 is signified by less than 0.8V and a 1 by greater than 2.5V. It accepts six data bits (DO through D5). This allows the numbers 0 through 63 (decimal) to convert to over five octaves of "keyboard" control when latched to the internal digital-to-analog converter (DAC) by the active low -DAC EN pulse. The GATE is exercised via a bit at pin 7.

  6. To play notes on the Pro-One, the system driving it will have to do something like the following. (The way in which these events happen is not so important as their sequence.) At the start, the analog KYBD CV output from the DAC (which controls the oscillators and filter) is unknown. Nothing is heard from the Pro-One because the envelope generators are not being gated. First the system somehow decides what key (out of 63) it wants to play. It then sets up the key number in binary form on D0-D5. (This might be done with a six-bit output port.) -DAC EN is normally high. To latch the key data to the DAC, -DAC EN is momentarily forced low. Data is then latched on the rising edge of this pulse. For practical purposes a delay of 20 microseconds will allow the DAC time to "settle" (worst-case). At this point, GATE can go high, triggering the envelope generators. When the note is to be turned off, it is likewise advisable to turn the GATE off (low) before again strobing the DAC.
  7. To return the Pro-One to normal operation, unplug your system from J101, remove R1182, cut the jumper installed in step 3 and carefully re-install U113, 8021.
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