HLASM Language Reference
HLASM Language Reference HLASM Language Reference
CCW1 Instruction data_count is an absolute expression that specifies the byte count or length of data. The value of this expression is right-justified in bytes 6 and 7 of the generated channel command word. The generated channel command word is aligned at a doubleword boundary. Any skipped bytes are set to zero. The internal machine format of a channel command word is shown in Figure 27. Figure 27. Channel Command Word, Format 0 Byte Bits Usage 0 0-7 Command code 1-3 8-31 Address of data to operate upon 4 32-37 Flags 38-39 Must be specified as zeros 5 40-47 Set to zeros by assembler 6-7 48-63 Byte count or length of data If symbol is an ordinary symbol or a variable symbol that has been assigned an ordinary symbol, the ordinary symbol is assigned the value of the address of the first byte of the generated channel command word. The length attribute value of the symbol is 8. The following are examples of CCW and CCW0 statements: WRITE1 CCW 1,DATADR,X'48',X'5' WRITE2 CCW 1,DATADR,X'48',X'5' The object code generated (in hexadecimal) for either of the above examples is: 1 xxxxxx 48 5 where xxxxxx contains the address of DATADR, and DATADR must reside below 16 megabytes. Using EXCP or EXCPVR access methods: If you use the EXCP or EXCPVR access method, you must use CCW or CCW0, because EXCP and EXCPVR do not support 31-bit data addresses in channel command words. Specifying RMODE: Use RMODE 24 with CCW or CCW0 to ensure that valid data addresses are generated. If you use RMODE ANY with CCW or CCW0, an invalid data address in the channel command word can result at execution time. CCW1 Instruction The CCW1 instruction defines and generates an 8-byte format-1 channel command word for input/output operations. A format-1 channel command word allows 31-bit data addresses. A format-0 channel command word generated by a CCW or CCW0 instruction allows only a 24-bit data address. If a control section has not been established, CCW1 will initiate an unnamed (private) control section. 116 HLASM V1R5 Language Reference
CCW1 Instruction ►►──┬────────┬──CCW1──command_code,data_address,flags,data_count───►◄ └─symbol─┘ 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 4-byte, A-type address constant. The value of this expression is right-justified in bytes 4 to 7 of the generated channel command word. flags is an absolute expression that specifies the flags for bits 8 to 15 of the generated channel command word. The value of this expression is right-justified in byte 1 of the generated channel command word. data_count is an absolute expression that specifies the byte count or length of data. The value of this expression is right-justified in bytes 2 and 3 of the generated channel command word. The generated channel command word is aligned at a doubleword boundary. Any skipped bytes are set to zero. The internal machine format of a channel command word is shown in Figure 28. Figure 28. Channel Command Word, Format 1 Byte Bits Usage 0 0-7 Command code 1 8-15 Flags 2-3 16-31 Count 4 32 Must be zero 4-7 33-63 Data address The expression for the data address should be such that the address is within the range 0 to 2 31 −1, inclusive, after possible relocation. This is the case if the expression refers to a location within one of the control sections that are link-edited together. An expression such as −1 yields an acceptable value only when the value of the location counter (*) is 1000000000 or higher at assembly time. Chapter 5. Assembler Instruction Statements 117
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CCW1 Instruction<br />
data_count<br />
is an absolute expression that specifies the byte count or length of data. The<br />
value of this expression is right-justified in bytes 6 and 7 of the generated<br />
channel command word.<br />
The generated channel command word is aligned at a doubleword boundary. Any<br />
skipped bytes are set to zero.<br />
The internal machine format of a channel command word is shown in Figure 27.<br />
Figure 27. Channel Command Word, Format 0<br />
Byte Bits Usage<br />
0 0-7 Command code<br />
1-3 8-31 Address of data to operate upon<br />
4 32-37 Flags<br />
38-39 Must be specified as zeros<br />
5 40-47 Set to zeros by assembler<br />
6-7 48-63 Byte count or length of data<br />
If symbol is an ordinary symbol or a variable symbol that has been assigned an<br />
ordinary symbol, the ordinary symbol is assigned the value of the address of the<br />
first byte of the generated channel command word. The length attribute value of<br />
the symbol is 8.<br />
The following are examples of CCW and CCW0 statements:<br />
WRITE1 CCW 1,DATADR,X'48',X'5'<br />
WRITE2 CCW 1,DATADR,X'48',X'5'<br />
The object code generated (in hexadecimal) for either of the above examples is:<br />
1 xxxxxx 48 5<br />
where xxxxxx contains the address of DATADR, and DATADR must reside below 16<br />
megabytes.<br />
Using EXCP or EXCPVR access methods: If you use the EXCP or EXCPVR<br />
access method, you must use CCW or CCW0, because EXCP and EXCPVR do<br />
not support 31-bit data addresses in channel command words.<br />
Specifying RMODE: Use RMODE 24 with CCW or CCW0 to ensure that valid<br />
data addresses are generated. If you use RMODE ANY with CCW or CCW0, an<br />
invalid data address in the channel command word can result at execution time.<br />
CCW1 Instruction<br />
The CCW1 instruction defines and generates an 8-byte format-1 channel command<br />
word for input/output operations. A format-1 channel command word allows 31-bit<br />
data addresses. A format-0 channel command word generated by a CCW or CCW0<br />
instruction allows only a 24-bit data address. If a control section has not been<br />
established, CCW1 will initiate an unnamed (private) control section.<br />
116 <strong>HLASM</strong> V1R5 <strong>Language</strong> <strong>Reference</strong>
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