kravitz@foxtail.com (Jody Kravitz) (06/27/91)
I am a hardware literate programmer interested in building a MIDI interface for my 68040 Cube. There has been some discussion in this group about using Macintosh MIDI interfaces with the Cube. Some reverse engineering has shown that several of the popular Macintosh MIDI interfaces get their power by operating a bridge rectifier off the TX+ and TX- data lines (clever, but YUCK!). This will not work with the '040 Cube, as it does not provide TX-. I will use an external power supply. The Macintosh MIDI interfaces that I have examined provide a 1MHZ clock signal to the Mac. This appearantly is divided by 32 in the Mac to provide the 31,250 HZ MIDI baud rate. There is a "Receive Clock" input signal in the Cube's serial port description, but there is no clue in any of the documentation (I have 2.0, not 2.1 documentation) as to when this signal is used. The 2.0 documentation gives little information on how the loadable MIDI driver actually talks to the serial port. Is the clock signal at 1MHZ required by the NeXT ? Does it belong on the "Receive Clock" pin ? The EXTA and EXTB clock rates as defined for stty()/ioctl() provide 19.2 and 38.4 KB baud rates. By what magic does the "MIDI Loadable Driver" arrange the 31,250 clock rate ? Can a Unix program not using a loadable driver use the "Receive Clock" input pin with an ioctl() ? If so, at what multiple of the baud rate should the clock be ? I'd appreciate e-mail responses as my news feed is often 48 hours behind. I'll post a summary of everything I receive. Thanks, Jody kravitz@foxtail.com or foxtail!kravitz@ucsd.edu ucsd!foxtail!kravitz