Specifications

170 Appendix B Logic Control—MIDI Implementation
Global Control Messages
Host Connection and Initialization
Received:
<Hdr> 00 F7
Device Query
<Hdr> 02 ss ss ss ss ss ss ss rr rr rr rr F7
Host Connection Reply
<Hdr> 0F 7F F7
Go Offline
Transmitted:
<Hdr> 01 ss ss ss ss ss ss ss ll ll ll ll F7
Host Connection Query
<Hdr> 03 ss ss ss ss ss ss ss F7
Host Connection Confirmation
<Hdr> 04 ss ss ss ss ss ss ss F7
Host Connection Error
ss = Serial number (7 bytes ASCII text, non null-terminated)
ll = Challenge code (4 bytes)
rr = Response code (4 bytes)
Offline Mode:
Logic Control employs a query system to maintain connection to the host software.
When Logic Control is initially powered up, it defaults to Offline mode. In Offline mode,
Logic Control’s faders move to their lowest setting, and the LCD reads “EMAGIC LOGIC
CONTROL -- by MACKIE.” After power-on, Logic Control also transmits a system
exclusive Host Connection Query message that is used by the host to detect a
connection, and what type of device is connected (Logic Control/Logic Control XT).
Communications Initialization:
When the host software receives a Host Connection Query message (containing a serial
number and a random challenge code), it should transmit a Host Connection Reply
command within 300ms to initialize Logic Control. The command must contain the
same serial number and the correct response code for the challenge code. Here is the
algorithm (l1 to l4 = challenge code bytes 1 to 4, r1 to r4 = response code bytes 1 to 4):
r1 = 0x7F & (l1 + (l2 ^ 0xa) - l4);
r2 = 0x7F & ((l3>>4) ^ (l1+l4));
r3 = 0x7F & ( l4-(l3<<2) ^ (l1|l2));
r4 = 0x7F & (l2-l3+(0xF0^(l4<<4)));
Logic Control will in turn respond with either a Host Connection Confirmation message
containing the serial number and switch to Online mode—where it will await further
instructions from the host, or reply with a Host Connection Error message in case the
response code was wrong.