Aviom A-16R/A-16CS User 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