HLASM Language Reference

DS Instruction
specified, the first storage area defined is addressable by the ordinary symbol.
The other storage areas can be reached by relative addressing.
operand
is an operand of six subfields. The first five subfields describe the attributes of
the symbol. The sixth subfield provides the nominal values that determine the
implicit lengths; however no constants are generated.
A DS operand has this format:
►►──┬────────────────────┬──type──┬────────────────┬────────────────►
└─duplication_factor─┘
└─type_extension─┘
►──┬──────────────┬──┬──────────┬──nominal_value───────────────────►◄
| └─program_type─ ┘ └─modifier─┘
The format of the DS operand is identical to that of the DC operand; exactly the
same subfields are used and are written in exactly the same sequence as they are
in the DC operand. For more information about the subfields of the DC instruction,
see “DC Instruction” on page 126.
Unlike the DC instruction, the DS instruction causes no data to be assembled.
Therefore, you do not have to specify the nominal value (sixth subfield) of a DS
instruction operand. The DS instruction is the best way of symbolically defining
storage for work areas, input/output buffers, etc.
Although the formats are identical, there are two differences in the specification of
subfields. They are:
The nominal value subfield is optional in a DS operand, but it is mandatory in a
DC operand. If a nominal value is specified in a DS operand, it must be valid.
The maximum length that can be specified for the character (C) and
hexadecimal (X) type areas is 65,535 bytes rather than 256 bytes for the same
DC operands. The maximum length for the graphic (G) type is 65,534 bytes.
If symbol denotes an ordinary symbol, the ordinary symbol, as with the DC
instruction:
Has an address value of the first byte of the area reserved, after any boundary
alignment is done
Has a length attribute value, depending on the implicit or explicit length of the
type of area reserved
If the DS instruction is specified with more than one operand or more than one
nominal value in the operand, the label addresses the area reserved for the field
that corresponds to the first nominal value of the first operand. The length attribute
value is equal to the length explicitly specified or implicit in the first operand.
Bytes Skipped for Alignment: Unlike the DC instruction, bytes skipped for
alignment are not set to zero. Also, nothing is assembled into the storage area
reserved by a DS instruction. No assumption should be made as to the contents of
the skipped bytes or the reserved area.
Chapter 5. Assembler Instruction Statements 175