Modal commands are arranged in sets called "modal groups", and only one member of a modal group may be in force at any given time. In general, a modal group contains commands for which it is logically impossible for two members to be in effect at the same time - like measure in inches vs. measure in millimeters. A machining center may be in many modes at the same time, with one mode from each modal group being in effect. The modal groups are shown in the following tables.
G0, G1, G2, G3, G38.2, G76, G80, G81, G82, G83, G84, G85, G86, G87, G88, G89
G17, G18, G19
Feed rate mode
G40, G41, G42
Cutter radius compensation
Tool length offset
Return mode in canned cycles
G54, G55, G56, G57, G58, G59, G59.1, G59.2, G59.3
Coordinate system selection
G61, G61.1, G64
Path control mode
XY plane rotation
M0, M1, M2, M30, M60
M54, M55, M56, M64, M65, M66
AUX and general purpose I/O
M3, M4, M5
M7, M8, M9
M48, M49, M50, M51, M52
Enable/disable feed and speed override switches
M90, M91, M92, M95, M97
Select standard or alternate spindle or touch probe or camera offset, M90 = standard
THC ON | THC OFF (Torch height control)
A axis clamp
Clamp on | clamp off
G4, G10, G28, G30, G53, G92, G92.1, G92.2, G92.3
For several modal groups, when a machining center is ready to accept commands, one member of the group must be in effect. There are default settings for these modal groups. The default values are automatically in effect when the machining center is turned on or otherwise re-initialized.
Group 1 is a group of G codes for motion. One of these is always in effect. That one is called the current motion mode.
It is an error to put a G-code from Group 1 and a G-code from Group 0 on the same line if both of them use axis words. If an axis word-using G-code from group 1 is implicitly in effect on a line (by having been activated on an earlier line), and a group 0 G-code that uses axis words appears on the line, the activity of the group 1 G-code is suspended for that line. The axis word using G-codes from group 0 are G10, G28, G30, and G92.