OPEN—List form

The list form of the OPEN macro constructs a data management parameter list. You can specify any number of parameters (DCB addresses and associated options).

There are two forms of the list, the short form and the long form. The short form list consists of a one-word entry for each DCB or ACB in the parameter list. The high-order byte is used for the options and the 3 low-order bytes are used for the DCB address. The long form list consists of an eight byte entry for each DCB or ACB in the parameter list. The high order byte is used for the options and the low order four bytes are used for the DCB or ACB address. For either form of list, the end of the list is indicated by a 1 in the high-order bit of the last entry's option byte. The length of a list generated by a list form instruction must be equal to the maximum length list required by any execute form instruction that refers to the same list. A maximum length list can be constructed by one of two methods:

Code a list-form instruction with the maximum number of parameters required by an execute form instruction that refers to the list.
Code a maximum length list by using commas in a list-form instruction to acquire a list of the appropriate size. For example, coding OPEN (,,,,,,,,,),MF=L would provide a list of 5 fullwords (5 DCB addresses and 5 options).

Entries at the end of the list not referred to by the execute-form instruction are assumed to have been filled in when the list was constructed or by a previous execute-form instruction. Before using the execute-form instruction, you can shorten the list by placing a 1 in the high-order bit of the last DCB entry to be processed.

A zeroed work area on a fullword boundary is equivalent to OPEN (,(INPUT,DISP),...),MF=L and can be used in place of a list-form instruction. Allocate four bytes per entry if you wish the effect of MODE=24. Allocate eight bytes per entry if you wish the effect of MODE=31. The high-order bit of the last DCB entry must contain a 1 before this list can be used with the execute-form instruction.

A parameter list constructed by an OPEN, list-form, macro can be referred to by either an OPEN or CLOSE execute form instruction. The description of the standard form of the OPEN macro explains the function of each parameter.

The list form of the OPEN macro is:

[label]

OPEN

([dcb address],[(options )],...) ,MF=L [,TYPE=J] [,MODE=24|31]

dcb address—A-Type Address

MF=L: specifies that the OPEN macro is used to create a data management parameter list that is referred to by an execute form instruction.
TYPE=J: coded the same as the standard form. This has no effect on the macro expansion.
MODE=24|31: coded the same as the standard form. This specification must match that of the execute form. Errors and unpredictable results occur if the modes are inconsistent.