MODCB—modify an access method control block

The format of the MODCB macro used to modify an access method control block follows.

The format of the MODCB macro used to modify an access method control block.

Label	Operand	Parameters
[`label`]	MODCB	ACB=`address` [BSTRNO=`abs expression`] [,BUFND=`abs expression`] [,BUFNI=`abs expression`] [,BUFSP=`abs expression`] [,DDNAME=`character string`] [,EXLST=`address`] [,MACRF=([ADR][,CNV] [,KEY] [,CFX\|NFX] [,DDN\|DSN] [,DFR\|NDF] [,DIR][,SEQ][,SKP] [,ICI\|NCI] [,IN][,OUT] [,NIS\|SIS] [,NRM\|AIX] [,NRS\|RST] [,NSR\|LSR\|GSR] [,NUB\|UBF])] [,MAREA=`address`] [,MLEN=`abs expression`] [,PASSWD=`address`] [,RMODE31={ALL\|BUFF\|CB\|NONE}] [,SHRPOOL=`abs expression`] [,STRNO=`abs expression`]

The subparameters of the MODCB macro can be expressed as absolute numeric expressions, as character strings, as codes, as expressions that generate valid relocatable A-type address constants, in register notation, as S-type address constants, and as indirect S-type address constants. Subparameters with GENCB, MODCB, SHOWCB, and TESTCB, further defines these operand expressions.

label: specifies 1 to 8 characters that provide a symbolic address for the MODCB macro.
ACB=address: specifies the address of the access method control block to be modified. The data set identified by the access method control block must not be opened. A request to modify the access method control block of an open data set will fail.

Important: The remaining parameters represent parameters of the ACB macro that can be modified. The value specified replaces the value, if any, presently in the access method control block. There are no defaults. For an explanation of these parameters, see ACB—generate an access method control block at assembly time.

If MODCB is used to modify a MACRF subparameter, other subparameters are unaffected, except when they are mutually exclusive. For example, if you specify MACRF=ADR in the MODCB and MACRF=KEY is already indicated in the control block, both ADR and KEY are now indicated. But, if you specify MACRF=UBF in the MODCB and NUB is indicated, only UBF will now be indicated.

The RMODE31 parameter tells the VSAM OPEN routines where to obtain storage for the control blocks and I/O buffers. Therefore, the only time the values specified by the RMODE31 parameter have any effect on VSAM is on the setting just before an OPEN is issued. At other times, changing these values has no effect on the residency of the control blocks and I/O buffers. RMODE31 is ignored for RLS processing.

If MODCB RPL is used to change the address of an ACB, you must first issue an ENDREQ macro.

Restriction: If you issue a MODCB for a non-VSAM and non-VTAM ACB, the results will be unpredictable.