Channel Command Words (CCW0 and CCW1)

The CCW0 instruction performs the same function as the CCW instruction, and is used to define and generate a format-0 channel command word that allows a 24-bit data address. The CCW1 instruction result is used to define and generate a format-1 channel command word that allows a 31-bit data address.

The format of the CCW0 and CCW1 instructions, like that of the CCW instruction, consists of a name field, the operation, and an operand (that contains a command code, data address, flags, and data count).

Using EXCP or EXCPVR access methods:

If you use the EXCP or EXCPVR access method, only CCW or CCW0 is valid, because EXCP and EXCPVR do not support 31-bit data addresses in channel command words.

Using RMODE ANY:

If you use RMODE ANY with CCW or CCW0, an invalid data address in the channel command word can result at execution time.