HLASM Language Reference

CCW and CCW0 Instructions
If several CATTR instructions within a source module have the same class name,
the first occurrence establishes the class and its attributes, and the rest indicate the
continuation of the text for the class. If you specify attributes on subsequent
CATTR instructions having the same class name as a previous CATTR instruction,
the assembler ignores the attributes and issues diagnostic message ASMA191W.
If you specify conflicting attributes on the same instruction, the assembler uses the
last one specified. In the following example, the assembler uses RMODE(ANY):
MYCLASS CATTR RMODE(24),RMODE(ANY)
Syntax Checking Only: If you code a CATTR instruction but don't specify the
GOFF or XOBJECT option, the assembler checks the syntax of the instruction
statement and does not process the attributes.
CCW and CCW0 Instructions
The CCW and CCW0 instructions define and generate an 8-byte, format-0 channel
command word for input/output operations. A format-0 channel command word
allows a 24-bit data address. The CCW and CCW0 instructions have identical
functions. If a control section has not been established, CCW and CCW0 will
initiate an unnamed (private) control section.
►►──┬────────┬──┬─CCW──┬────────────────────────────────────────────►
└─symbol─┘
└─CCW─┘
►──command_code,data_address,flags,data_count──────────────────────►◄
symbol
is one of the following:
An ordinary symbol
A variable symbol that has been assigned a character string with a value
that is valid for an ordinary symbol
A sequence symbol
command_code
is an absolute expression that specifies the command code. This expression's
value is right-justified in byte 0 of the generated channel command word.
data_address
is a relocatable or absolute expression that specifies the address of the data to
operate upon. This value is treated as a 3-byte, A-type address constant. The
value of this expression is right-justified in bytes 1 to 3 of the generated
channel command word.
flags
is an absolute expression that specifies the flags for bits 32 to 37, and zeros for
bits 38 and 39, of the generated channel command word. The value of this
expression is right-justified in byte 4 of the generated channel command word.
Byte 5 is set to zero by the assembler.
Chapter 5. Assembler Instruction Statements 115