shown in Figure 3.
The Home Screen displays are:
USB Status: The “cactus” — six characters from the
end of the first row is my low-res attempt at the USB symbol. It is displayed when mistralXG is connected to your
PC. The next five symbols show the status of the user
options (discussed later).
Error Status: The space to the left of the USB symbol
shows the global error flag and is normally blank. If an
error occurs, this changes to an “!” and the error screens
Real-time MIDI Activity Monitor: The second row
shows MIDI IN (top line) and MIDI OUT (bottom line)
activity. Figure 2 shows the data being transmitted from
the PC on channels 1, 3, 5, 6, 7, and 10 (left to right). No
data is being transmitted to the PC (all channels are low
on the top line). The MIDI IN monitor remains active even
when mistralXG is not connected to your PC.
The remaining screens allow you to access user
options and are displayed by pressing the SELECT button.
The SET button changes settings or performs some other
useful action. From the Home and Splash screens, SET
provides quick access to useful features (see Figure 4). No
matter which screen is being displayed, after a few seconds without a button being pressed, the display returns
to the Home Screen.
SELECT cycles through the various screens, as shown
in Figure 4. Pressing SET toggles or otherwise modifies the
setting for each particular screen. I’ve already discussed
the Home Screen, so now let’s take a look at the others.
The first two screens allow you to select which MIDI
stream is transmitted to the synthesizer. The first option
flag on the Home Screen (“U” in Figure 3) shows which
stream has been selected. Screen 1 lets you choose
between the MIDI IN and WX IN inputs (Switch 1 in
Figure 1), while Screen 2 selects between the output of
Switch 1 and USB data from the PC (Switch 2 in
1). The display shows “M,” “W,” or “U,” depending on
your choices. If USB is selected and mistralXG is not
plugged into your computer, Switch 2 automatically
selects your M/W choice, reverting to U when the USB
connection is reactivated.
Screens 3 and 4 control the MIDI THRU and MIDI
OUT streams respectively. When enabled, MIDI THRU
receives the M or W stream coming from Switch 1. MIDI
OUT echoes the MIDI stream coming from the PC.
Selecting Disable in these screens switches their respetive
Screen 5 controls MIDI Running Status. This feature of
MIDI reduces the amount of data transmitted. It works on
the principle that if a status byte would be repeated, it can
be omitted. So, if consecutive MIDI commands are all
“Note on, channel 5” (0x94 as already seen), then the
command byte is omitted for subsequent notes until a
new status byte is required. This reduces the amount of
data transmitted by 10% to 15%. Normally, Running
Status should be enabled, but you could disable it if you
think it may be causing problems for a receiving device.
Certain byte sequences are invalid MIDI commands.
A receiving device should ignore these, so filtering shouldn’t be necessary. If you think invalid messages may be
causing problems, however, the filter can be enabled in
Screen 6. Invalid sequences are reported as errors by
mistralXG, whether or not the filter is active.
Screen 7 is not normally displayed. It shows the error
types that have occurred, and only becomes available
when an error has been registered. In this case, the Home
Screen global error flag is displayed (see Figure 4).
Pressing SET while on Screen 7 shows the individual error
screens. A second press of SET resets the specific counter.
After zeroing a counter, pressing SET once more
allows you to clear all error counters and return to the
Home Screen. If you’d rather examine the individual error
Here are a few links that I have found useful. Links come and
go, of course. If that happens, just load a few key words into your
favorite search engine and you’ll find lots out there.
MIDI specifications: www.midi.org (unfortunately, these have
to be purchased, but web sources are almost as good). There are
hundreds of MIDI-related sites on the Internet. These are just a
couple of the top hits from Google:
USB Specifications: www.usb.org. Here you can find both
the USB 2.0 spec (650 odd pages!) and more specific documents,
including the USB-MIDI spec.
USB in a Nutshell:
There are many websites describing these popular displays.
Here are just a couple:
PIC MCU Information:
PIC Discussion Group:
February 2009 47