Corection > Btw. the diode that is upside down to the opto-coupler diode at some > MIDIinterfaces, seems to eliminate the positive side of the electric > wave, to get a better slew rate for the negative side, because MIDI > seems to use the negative side only.
Hm? The diode seems to be for a steeper slew rate, but it seems to be a freewheeling diode. Quentin seems to be right, that for this usage a Schottky diode is the right choice and not a normal diode. This seems to be a fact, but the by me above mentioned physical principles might be nonsense, dunno. Some C64 MIDI interfaces are using a normal diode, the 1N4148 and instead of a 220 ohm resistor a 100 ohm one for MIDI in. It's written, that the 1N4148 should be fast and should be also fine for such usage. Without this information a friend (the electric technician) said to me, after I told him what diodes I've got on stock, that I should use a 1N4148, even if Quentin is right, a 1N4148 seems to be also right and more common. Meanwhile I guess it doesn't matter what circuit diagram is used, as long as there is an opto-coupler, some resistors, any fast diode and a TTL gate. "MIDI-DIN Electrical Specification": http://www.midi.org/techspecs/electrispec.php They are using a 1N914 diode (1N4148, 1N4448, 1N914, 1N914B seems to have the same technical data). "MIDI Standard Hardware NOTES: 1. Opto-isolator shown is Sharp PC-900. HP 6N138 or other can be used with changes." I guess this means that a 100 ohm or 220 ohm resistor is used depending to the used opto-coupler. All available commercially MIDInterfaces seems to be fine and circuit diagrams without TTL gates for the output might be fine for some sound cards, that have TTL gates behind the UART or ACIA on their boards. Today I guess that jitter mainly is a software problem. Btw. for serial interface usage the UART should be better than the ACIA for the C64 and they need IRQ priority to avoid data loss, for modern computers I never heard of the ACIA, but only of the UART. The MPU401 is using an UART, the Envy24 is using MPU401 etc.. From this hardware side everything seems to be fine for modern computers and the hardware possibly is better than some MIDInterfaces for old computers. I guess I was wrong with thinking that modern interfaces sometimes might be bad. Jitter might come from chip sets on mobos and the software, but unlikely from the MIDInterfaces. _______________________________________________ 64studio-users mailing list [email protected] http://lists.64studio.com/mailman/listinfo/64studio-users
