Aviom A-16R/A-16CS - Manual (Page 84)

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2.2. MIDI System Exclusive Packet Tail
Every complete MIDI System Exclusive message should contain a Trailer/
Tail byte referred to as an “End of Exclusive” or EOX for short. Reception of
implemented System Exclusive messages in the A‑16R that do not contain an
EOX will be treated as incomplete and flagged as an error.
EOX 1111 0111 (F7H) End of Exclusive
2.3. Message Data Format
There are essentially two basic data byte formats used in the “Message Data”
section of an A‑16R’s SysEx message. The first format is a nibblized format
and the second is a padding format. In general the “Message Data” of the
A‑16R’s SysEx message is nibbilized or broken up into MIDI seven bit status
bytes. In this nibblization process one data byte becomes two bytes. The
upper 4 Bits or upper nibble of the first byte is fixed while the lower 4 Bits or
lower nibble contains the Most Significant Bits (MSB) of the data byte being
“nibblized.” Similarly, the upper nibble of the second byte is fixed while the
lower nibble contains the Least Significant Bits (LSB) of the data byte.
MSB 0001 hhhh h = high 4 bits of data byte ‑ sent first
LSB 0001 llll l = low 4 bits of data byte
The second basic data byte format used in the “Message Data” section is the
padding format. Padding is inserted between presets in order to provide
necessary delays to allow for preset processing.
Padding 0000 0000 (00H) Padding byte format, ignored
by A‑16R
2.4. Checksum Calculation
The preset checksum is calculated by a straight 8‑Bit addition of all preset
data bytes, excluding the preset ID, prior to nibblization. In the event of an
overflow the overflow will be discarded in this scheme. Once the checksum
has been calculated, the 8‑ Bit result is then nibblized for transmission and
inserted into the MIDI SysEx message. In the case of the All Presets Message
several checksums are included in the MIDI SysEx message, one for each
preset contained within the message.
2.5. Receiver Errors
Many events may result in errors being generated. For example, if the
received checksum doesn’t match the calculated checksum or if reception
of a channel voice message occurs in the middle of a SysEx message, a SysEx