IBM TS3500 Manual page 116

A D23 or D53 frame with multiple I/O stations assigns its I/O slot addresses as if the
multiple stations were one. For example, in a D-frame:
• An I/O slot address of F02,R05 means frame 1, slot 5 (indicates the fifth row from
the top of the upper left I/O station)
• An I/O slot address of F04,R40 means frame 3, slot 8 (indicates the eighth row from
the top of the upper right I/O station)
Note: Because the L-frame is always frame number F01, D-frame numbers begin with F02.
(see Figure 2)
Figure 2. Storage slot addresses in four I/O station frames in the TS3500 Tape Library. The
door of a Model D23 frame is shown.