DigiTech Midi Implementation Manual page 123

GSP21
0 - 127 Program 1 - 128
128 Repeat Hold
129 FX Loop Bypass
GSP21 PRO
0 - 191 Program 1-192
192 Repeat Hold
193 FX Loop Bypass
Active foot controller set (0-9)
0 Foot switch set 1 is active
. .
8 Foot switch set 9 is active
9 Foot switch set 0 is active (10)
Note: Pointer to active foot controller must also be set if this byte is
changed
Pointer to active foot controller definition
Byte 1 = (active foot controller set * 10 + 6,933) / 256
Byte 2 = (active foot controller set * 10 + 6,933) MOD 256
5/10 Patch mode flag (0 - 1)
0 Foot switch in 5 patch mode
1 Foot switch in 10 patch mode