OS_Mgb, get current bank binding in segment

RST 20H, DEFB $5A

IN:

     C = memory segment specifier (MS_S0, MS_S1, MS_S2 & MS_S3)

     Fc = 0
     B = bank number currently bound to that segment
     C = C(in)

     Fc = 1
     A = error code:
          RC_ERR ($0F), C was not valid

     ...CDEHL/IXIY same
     AFB...../.... different

Bugs:
 

Related calls:

OS_Bix, Bind in extended address
OS_Box, restore bindings after OS_Bix
OS_Fc, select fast code (fast bank switching)
OS_Mal, allocate memory
OS_Mcl, close memory (free memory pool)
OS_Mfr, free (previously allocated block) memory
OS_Mop, open memory (allocate memory pool)
OS_Mpb, set new bank binding in segment