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MegaDisc 07 (1988)(MegaDisc Digital Publishing)(AU)[WB].zip
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MUSIC
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Midi_2000&500
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2000-04-10
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60 lines
NOTES ON MIDI INTERFACE FOR AMIGA 2000
by Steve Shergis
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Ed: Steve Wright gave full details on MD4 about how to build a do-it-
yourself MIDI interface for the A1000, along with a DPaint graphic.
Numerous people have built it and it works like a dream. Steve may
provide us with a few more hardware hacks as time goes on. Steve
and Doug have edited Steve Wright's DPaint illustration to show the
modifications described here, and we'll put it into the next MD if
there is a demand for it - call us.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
These notes are written to explain the modifications which have been
made to Steve Wright's Midi circuit from Megadisc 4 to adapt it for use
with an Amiga 2000. I have not yet had time to try this with an Amiga
500 but according to the pin configurations in the book it SHOULD work.
1. Since there is no 5 volt rail available on pin 21 of the Amiga 2000
serial connector the only other source of power for the interface was
available on pin 9. This is a 12 volt supply and should be regulated to
+5 volts to drive the Midi interface.
NOTE - The 12 volt output from the Amiga 2000 is just adequate to drive
this unit however you will notice that the 12 volt rail will drop to
about 8 volts when driving the interface. This appears to have no
deleterious effect on the Amiga power supply.
WARNING - Do not use a zener diode in place of the three terminal
regulator as this will pull the 12 volt rail down to +5 volts and this
may damage the 12 volt rail.
2. If you have looked at the previous circuit on Megadisc 4 you will
notice capacitors 1 to 4 have also been added to the circuit as well as
another LED. 1 and 2 are used in conjunction with the regulator (LM7805)
as filter capacitors. 3 and 4 are by-pass capacitors and must be
connected as close as practicable to power supply pins on IC 1 and 2. A
power/on LED has been included .
NOTE - Use a high efficiency Red LED and do not use a series resistor
(R8) less than 4.7k ohm as this will unnecessarily load the power supply.
3. The regulator used is a standard 3 terminal 5 volt device. Please note
pin configuration: Pin 1 IN
Pin 2 Earth
Pin 3 OUT
Pin 1 to 3 runs left to right on the package. Failure to do this will
cause damage to the regulator and possibly your Amiga!
WARNING : When making up MIDI (Din) leads follow this wiring procedure.
Pin 4 to pin 4, Pin 2 to Pin 2 and Pin 5 to Pin 5.
*****************************************************************