DCB for GAM

Common Name:

Data Control Block for GAM

Macro Name:

DCBD

DSECT Name:

IHADCB

Owning Component:

Data Management, subcomponent OPEN/CLOSE/EOV

Eye-Catcher ID:

None

Subpool and Key:

Problem program subpool and key

Size:

52 bytes

Created by:

Problem program

Pointed to by:

DEBDCBAD field of the DEB data area
IOBDCBPT field of the IOB data area

Serialization:

None

Function:

This data control block (DCB) is used by the graphics access method (GAM) routine. The GAM access method uses the common DCB interface and foundation sections used by all other access method routines, although some differences might exist. An interface section with information about a particular graphics device precedes the common section.

Offset	Type/Value	Len	Name (Dim)	Description
DATA CONTROL BLOCK DEFINITION
	X'80'		DCBBIT0	"128"
	X'40'		DCBBIT1	"64"
	X'20'		DCBBIT2	"32"
	X'10'		DCBBIT3	"16"
	X'8'		DCBBIT4	"8"
	X'4'		DCBBIT5	"4"
	X'2'		DCBBIT6	"2"
	X'1'		DCBBIT7	"1"
GRAPHIC DEVICE INTERFACE
0 (0)	BITSTRING	12		– RESERVED
12 (C)	ADDRESS	2	DCBBRSA	– BUFFER RESTART ADDRESS. BLANK BEFORE EXECUTION OF SECOND I/O OPERATION
14 (E)	CHARACTER	1	DCBGTYPE	– TYPE OF BUFFER MANAGEMENT AND ATTENTION HANDLING
	. . . . . . . .		DCBGTEXP	"X'00'"– EXPRESS
	. . . . . . .1		DCBGTBAS	"X'01'"– BASIC
	. . . . . .1.		DCBGTNBM	"X'02'"– DEFAULT – NO BUFFER MANAGEMENT
15 (F)	BITSTRING	1		– RESERVED
16 (10)	ADDRESS	2	DCBBFRST	– BLANK BEFORE EXECUTION OF OPEN ROUTINE. STARTING ADDRESS FOR BUFFER AFTER EXECUTION OF OPEN ROUTINE
18 (12)	SIGNED	2	DCBBFRSZ	– BLANK BEFORE EXECUTION OF OPEN ROUTINE. SIZE OF BUFFER AFTER EXECUTION OF OPEN ROUTINE.
COMMON INTERFACE
20 (14)	BITSTRING	6		– RESERVED
26 (1A)	BITSTRING	2	DCBDSORG (0)	– DATA SET ORGANIZATION BEING USED
26 (1A)	BITSTRING	1	DCBDSRG1	– FIRST BYTE OF DCBDSORG
	1. . . . . . .		DCBDSGIS	"DCBBIT0"– IS – INDEXED SEQUENTIAL ORGANIZATION
	.1. . . . . .		DCBDSGPS	"DCBBIT1"– PS – PHYSICAL SEQUENTIAL ORGANIZATION
	. .1. . . . .		DCBDSGDA	"DCBBIT2"– DA – DIRECT ORGANIZATION
	. . .1 . . . .		DCBDSGCX	"DCBBIT3"– CX – BTAM OR QTAM LINE GROUP
	. . . . . .1.		DCBDSGPO	"DCBBIT6"– PO – PARTITIONED ORGANIZATION
	. . . . . . .1		DCBDSGU	"DCBBIT7"– U – UNMOVABLE, THE DATA CONTAINS LOCATION DEPENDENT INFORMATION
27 (1B)	BITSTRING	1	DCBDSRG2	– SECOND BYTE OF DCBDSORG
	1. . . . . . .		DCBDSGGS	"DCBBIT0"–GS – GRAPHICS ORGANIZATION
	.1. . . . . .		DCBDSGTX	RESERVED
	. .1. . . . .		DCBDSGTQ	RESERVED
	. . . . 1. . .		DCBACBM	"DCBBIT4"– ACCESS METHOD CONTROL BLOCK
	. . . . .1. .		DCBDSGTR	RESERVED
28 (1C)	ADDRESS	4	DCBIOBAD	– BLANK BEFORE EXECUTION OF OPEN ROUTINE. ADDRESS OF STANDARD FIELDS OF FIRST IOB AFTER EXECUTION OF OPEN ROUTINE
FOUNDATION EXTENSION
32 (20)	ADDRESS	4	DCBPOLST (0)	– ADDRESS OF AREA WHERE A DCB LIST IS TO BE CONSTRUCTED FOR POLLING PURPOSES
32 (20)	SIGNED	1	DCBGNCP	– NUMBER OF I/O INSTRUCTIONS TO BE ISSUED BEFORE A WAIT MACRO INSTRUCTION
33 (21)	ADDRESS	3	DCBPOLSA	– SAME AS DCBPOLST ABOVE
36 (24)	ADDRESS	4	DCBEXLST (0)	– ADDRESS OF USER'S EXIT LIST
36 (24)	BITSTRING	1		– RESERVED
37 (25)	ADDRESS	3	DCBEXLSA	– ADDRESS OF USER'S EXIT LIST
FOUNDATION BEFORE OPEN
40 (28)	CHARACTER	8	DCBDDNAM	– 8–BYTE NAME FROM DD STATEMENT THAT DEFINES DATA SET ASSOCIATED WITH THIS DCB
48 (30)	BITSTRING	1	DCBOFLG	– FLAGS USED BY OPEN ROUTINE
	1. . . . . . .		DCBOFGRW	"DCBBIT0"– IF ZERO, LAST I/O OPERATION WAS GREAD. IF ONE, LAST I/O OPERATION WAS GWRITE.
1	. .1. . . . .		DCBOFEOV	"DCBBIT2"– SET TO 1 BY EOV WHEN IT CALLS CLOSE ROUTINE FOR CONCATENATION OF DATA SETS WITH UNLIKE ATTRIBUTES
	. . .1 . . . .		DCBOFOPN	"DCBBIT3"– AN OPEN HAS BEEN SUCCESSFULLY COMPLETED
1	. . . . 1. . .		DCBOFPPC	"DCBBIT4"– SET TO 1 BY PROBLEM PROGRAM TO INDICATE A CONCATENATION OF UNLIKE ATTRIBUTES
	. . . . .1. .		DCBOFTM	"DCBBIT5"– TAPE MARK HAS BEEN READ
1	. . . . . .1.		DCBOFUEX	"DCBBIT6"– SET TO 0 BY AN I/O SUPPORT FUNCTION WHEN THAT FUNCTION TAKES A USER EXIT. SET TO 1 ON RETURN FROM USER EXIT TO THE I/O SUPPORT FUNCTION WHICH TOOK THE EXIT.
	. . . . . . .1		DCBOFIOF	"DCBBIT7"– SET TO 1 BY AN I/O SUPPORT FUNCTION IF DCB IS TO BE PROCESSED BY THAT FUNCTION
49 (31)	BITSTRING	1	DCBIFLG	– SET TO ZERO BY GRAPHIC ROUTINES BUT USED BY IOS IN COMMUNICATING ERROR CONDITIONS AND IN DETERMINING CORRECTIVE PROCEDURES
50 (32)	BITSTRING	2	DCBMACR (0)	– MACRO INSTRUCTION REFERENCE
50 (32)	BITSTRING	1	DCBMACR1	– FIRST BYTE OF DCBMACR
	. .1. . . . .		DCBMRRD	"DCBBIT2"– READ
	. . . . . .1.		DCBMRCRL	"DCBBIT6"– CNTRL
51 (33)	BITSTRING	1	DCBMACR2	– SECOND BYTE OF DCBMACR
	. .1. . . . .		DCBMRWRT	"DCBBIT2"– WRITE
	. . . . . .1.		DCBMRCTL	"DCBBIT6"– CNTRL
FOUNDATION AFTER OPEN
40 (28)	ADDRESS	2	DCBTIOT	– OFFSET FROM TIOT ORIGIN TO DD ENTRY ASSOCIATED WITH THIS DCB
42 (2A)	BITSTRING	2	DCBMACRF (0)	– SAME AS DCBMACR BEFORE OPEN
42 (2A)	BITSTRING	1	DCBMACF1	– FIRST BYTE OF DCBMACRF
43 (2B)	BITSTRING	1	DCBMACF2	– SECOND BYTE OF DCBMACRF
44 (2C)	ADDRESS	4	DCBDEBAD (0)	– ADDRESS OF ASSOCIATED DEB
44 (2C)	BITSTRING	1	DCBIFLGS	– SAME AS DCBIFLG BEFORE OPEN
45 (2D)	ADDRESS	3	DCBDEBA	– ADDRESS OF ASSOCIATED DEB
48 (30)	ADDRESS	4	DCBGIOCR (0)	– ADDRESS OF GRAPHICS I/O CONTROL ROUTINE
48 (30)	BITSTRING	1	DCBOFLGS	– SAME AS DCBOFLG BEFORE OPEN
49 (31)	ADDRESS	3	DCBGIOCA	– ADDRESS OF GRAPHICS I/O CONTROL ROUTINE