HLASM: V1R6 Language Ref

CCW and CCW0 instructionssupport 31-bit data addresses in channel command words.End of z/OSSpecifying RMODE: Use RMODE 24 with CCW or CCW0 to ensure that valid dataaddresses are generated. If you use RMODE ANY with CCW or CCW0, an invaliddata address in the channel command word can result at execution time.CCW1instructionThe CCW1 instruction defines and generates an 8-byte format-1 channel commandword for input/output operations. A format-1 channel command word allows31-bit data addresses. A format-0 channel command word generated by a CCW orCCW0 instruction allows only a 24-bit data address. If a control section has notbeen established, CCW1 will initiate an unnamed (private) control section.►►symbolCCW1 command_code,data_address,flags,data_count ►◄symbolis one of the following:v An ordinary symbolv A variable symbol that has been assigned a character string with a value thatis valid for an ordinary symbolv A sequence symbolcommand_codeis an absolute expression that specifies the command code. This expression’svalue is right-justified in byte 0 of the generated channel command word.data_addressis a relocatable or absolute expression that specifies the address of the data tooperate upon. This value is treated as a 4-byte, A-type address constant. Thevalue of this expression is right-justified in bytes 4 to 7 of the generatedchannel command word.flagsis an absolute expression that specifies the flags for bits 8 to 15 of thegenerated channel command word. The value of this expression isright-justified in byte 1 of the generated channel command word.data_countis an absolute expression that specifies the byte count or length of data. Thevalue of this expression is right-justified in bytes 2 and 3 of the generatedchannel command word.The generated channel command word is aligned at a doubleword boundary. Anyskipped bytes are set to zero.Chapter 5. Assembler instruction statements 115