9. COORDINATE VALUE
There are two ways to command travels of the tool; the absolute
command, and the incremental command. In the absolute command,
coordinate value of the end position is programmed; in the incremental
command, move distance of the position itself is programmed. G90
and G91 are used to command absolute or incremental command,
Absolute programming or incremental programming is used depending
on the command used. See following tables.
G code system A B or C
Command method Address word G90, G91
Absolute command Incremental command
X axis move command
Z axis move command
Y axis move command
C axis move command
G90 _ ;
G91 _ ;
D G code system B or C
G code system A G code system B or C
Absolute command X400.0 Z50.0 ; G90 X400.0 Z50.0 ;
Incremental command U200.0 W–400.0 ; G91 X200.0 Z–400.0 ;
1 Absolute and incremental commands can be used together
in a block.
In the above example, the following command can be
X400.0 W–400.0 ;
2 When both X and U or W and Z are used together in a block,
the one specified later is effective.
3 Incremental commands cannot be used when names of the
axes are A and B during G code system A is selected.
D G code system A
D Tool movement from point
P to point Q (diameter
programming is used for