Gilderfluke&Co BR-SmartMedia - Manual (Page 64)

ration mode exited, the BR-SmartMedia will start monitoring for
any changes in these sixteen bytes. Any bit that goes high will trig-
ger a MIDI ‘key down’ string to be sent. Any bit that was high and
goes low will trigger a MIDI ‘key up’ string.
Normal keyboards only have 88 keys. The 128 digitals moni-
tored by the BR-SmartMedia are mapped with a standard key-
board right in the middle. Middle ‘C’ is found on the 60th digital.
This translates to bit four of the seventh byte that is being moni-
tored.
Each of the MIDI key up/key down strings is three bytes long.
At the relatively slow 31,250 baud rate MIDI uses (3125 bytes per
second), it is possible to overrun the 256 byte long buffer used for
sending data from the BR-SmartMedia. Be aware that the low
speed of a MIDI serial stream means that it will take almost 1/10 of
a second to send out 256 bytes of data. The following are the
rules for MIDI:
1) Don’t make more than 85 key changes on any one frame
of animation data. The last bits won’t be turned on or off
until almost 1/10th of a second later (3 frames after the first
bit changed, at thirty FPS).
2) You can not send more than 1041 MIDI key up/key down
sequences per second.
3) At thirty FPS, the average number of changes on each
frame should not exceed 34.
4) MIDI has no error detection or correction built in. There is no
guarantee that any command will ever reach the device
that the BR-SmartMedia is controlling through a MIDI output.
If a MIDI ‘key down’ sequence is missed, the output will re-
main off until another MIDI ‘key down’ is received for the
same output. If a MIDI ‘key up’ sequence is missed, the out-
put will remain stuck on until another MIDI ‘key up’ is re-
ceived for the same output. Do not use MIDI for any safety
related equipment.
5) MIDI wiring standards allow for a MAXIMUM wire length of
fifty feet. The longer the wire, the better are the chances
that MIDI messages will be missed or garbled. A MIDI re-
ceiver can’t tell a garbled MIDI message from a perfectly
good one.
The above are all shortcomings in the design of any MIDI sys-
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