HP 3000 Manuals

Introduction to MPE XL for MPE V Programmers Migration Guide

FREADBACKWARD 
(not used) 

You can use the FREADBACKWARD intrinsic only with magnetic tape drives
that have "Read Reverse" capability.  Because MPE XL does not currently
support magnetic tape devices that have the "Read Reverse" capability,
calls to FREADBACKWARD will result in an error (condition code set to
CCL).

MPE/iX 5.0 Documentation