Emax

Has there been any progress with the USB to synchronous RS-422
interface?

My work on the synchronous RS-422 to asynchronous RS-422 converter ran
aground when I found the microcontroller was unable to handle the
number of interrupts generated by bidirectional communication at 500k
baud. The interface also needs to handle the baud rate switching on
the Emax side itself by either monitoring the transfer protocol or by
receiving some non-Emax sysex messages from the PC host.

The potential issues with either of these options mean extensive
debugging and ongoing upgrades to firmware would probably be required.
However, I believe it would be possible for the host PC side to use an
RS-232 port with auto baud rate setting, so it could potentially work
with any USB to RS-232 or built in RS-232 interface. Anyway, to move
forward I will need to upgrade to a faster microcontroller which will
also allow for in circuit flash upgrade of firmware. But if the USB
alternative is already working then there may not be too much point.

I found a copy of the Emax 2 MIDI and RS-422 specifications which I
have scanned and uploaded to the files section. It details the 12 bit
and 16 bit high speed sample transfer protocols as well as the Emax
bank image transfer protocol. It appears the Emax 2 was designed to be
compatible with the RS-422 CDROM drive after all! It also explains
differences between the implementations on the Emax and Emax 2 as well
as some Emax 2 bugs and corrections in various OS revisions. I also
have hardware information on the Macintosh serial interface that the
Emax is designed to interface with, but I have not uploaded it yet.

/Tristan