HEIDENHAIN iTNC 530 HSCI Technical Manual page 1624

S → S,
Single changing
arm, M4540 = 0 or
MP7481.x, bit x = 0
1624
First the pocket number of the old tool and the tool number zero are
transferred.
Zero means clear the spindle!
Acknowledge with M4093.

Then the pocket number and tool number of the new tool are transferred.
HEIDENHAIN Technical Manual iTNC 530 HSCI