HEIDENHAIN iTNC 530 HSCI Technical Manual page 1626

N → S:
Special tool follows
a normal tool
N → S,
Single changing
arm, M4540 = 0 or
MP7481.x, bit x = 0
1626
With this change sequence, two pocket numbers or two tool numbers must
be transferred in succession. M4520 indicates that another TOOL CALL strobe
(M4073) will follow. Regardless of M4541, there is a different sequence for
the pocket number transfer for single and double-arm changers (M4540 or
MP7481.x).
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