This macro moves the specified general tape backward over a specified
number of physical blocks.
Format
- label
- A symbolic name can be assigned to the macro statement.
- NAME
- Specifies the symbolic general tape name. It can be:
- yyy
- A three-character string representing a symbolic general tape name.
The first two characters must be alphabetic, and the third character must be
alphabetic or numeric. For general tapes, the first two characters
cannot be RT.
- (Rn)
- The number of a register containing a pointer to the symbolic real-time
tape name. n must be a decimal number from 0 through 7, 14, or
15.
- LEVEL=Dx
- A symbolic data level (D0-DF) must be specified.
- ERROR=label
- The label of an operational program error routine within the current
program segment must be specified.
- F
- An optional keyword parameter can be specified indicating whether fallback
to a previous volume is to be allowed when processing multivolume
files. This will occur when an attempt is made to backspace a tape past
the load point.
- YES
- Fallback is to be allowed.
- NO
- Fallback is to be inhibited.
If omitted, a default of YES is assumed.
The following macro format is still supported:
- label
- A symbolic name can be assigned to the macro statement.
- name
- A 3-character symbolic general tape name must be specified as the first
parameter.
- Dx
- A symbolic data level (D0-DF) must be specified as the second
parameter.
- error_branch
- The label of an operational program error routine within the current
program segment must be specified as the third parameter.
- F
- An optional keyword parameter can be specified indicating whether fallback
to a previous volume is to be allowed when processing multivolume
files. This will occur when an attempt is made to backspace a tape past
the load point.
- YES
- Fallback is to be allowed.
- NO
- Fallback is to be inhibited.
If omitted, a default of YES is assumed.
Entry Requirements
- R9 must contain the address of the ECB being processed.
- The general tape specified by this macro must be open when this macro is
issued.
- The number of physical blocks to be backspaced must be contained in the
low-order 2 bytes of the file address reference word (FARW) of the data level
specified by this macro. This number cannot be zero and cannot exceed
65 535. Attempts to backspace more than 65 535
records will backspace the number of records equal to the value entered mod 64
K.
Return Conditions
- If no I/O hardware errors or unusual conditions have occurred, control is
returned to the next sequential instruction (NSI). Otherwise, control
is returned to the error routine.
- The contents of R14 and R15 are unknown. The contents of all other
registers are preserved across this macro call.
- All pending I/O operations (including this request) are complete for this
ECB.
- For I/O hardware errors, the system error routine has taken a storage dump
and informed CRAS.
Programming Considerations
- This macro can be executed on any I-stream.
- Both keyword and positional parameters may be used in the same macro
call. This practice is not recommended.
- This macro cannot be used to backspace a blocked tape. If
backspacing is attempted with a blocked tape, a system error is issued.
Examples
None.