Programming Interface Information: This information is NOT intended to be used as Programming Interfaces of z/VM.

#### MEXBK

Prolog

Control Block Contents
MEXBK DSECT
MEXENTRY DSECT

Storage Layout

Cross Reference (Contains links to field and bit definitions)

#### MEXBK Prolog

     NAME       : HCPMEXBK
     DESCRIPTION: MULTIPLE EXPOSURE BLOCK
     DSECT      : MEXBK
     FUNCTION   : CONTAINS THE NECESSARY INFORMATION TO FIND EACH EXPOSURE
                  FOR MULTIPLE EXPOSURE DEVICES.
     LOCATED BY : RDEVEXPB FIELD OF RDEV  - POINTER TO MEXBK
     CREATED BY : HCPRDAAT - DURING ATTACH OF A MULTIPLE EXPOSURE DASD DEVICE
     DELETED BY : HCPRDADT - DURING DETACH OF A MULTIPLE EXPOSURE DASD DEVICE

#### MEXBK Control Block Content

#### MEXBK DSECT

####

####

####

    Hex   Dec Type/Val   Lng Label (dup)    Comments
    ---- ---- --------- ---- -------------- --------
    0000    0 Structure      MEXBK          MULTIPLE EXPOSURE BLOCK
    0000    0 Bitstring    1 MEXCTEXP       Count of exposure blocks.
    0001    1 Bitstring    1 *              Reserved for IBM use.
         This is information for multiple exposure blocks. This information
         indicates what exposure to use next for the reads or writes.
    0002    2 Bitstring    6 MEXRDWRI (0)
    0002    2 Bitstring    1 MEXFRDEX       First read exposure
    0003    3 Bitstring    1 MEXLRDEX       Last read exposure
    0004    4 Bitstring    1 MEXCREAD       Current available read exposure
         These are the write exposures.
    0005    5 Bitstring    1 MEXFWREX       First available write exposures
    0006    6 Bitstring    1 MEXLWREX       Last write exposure
    0007    7 Bitstring    1 MEXCWRIT       Current available write exposure
    0008    8 Address      4 MEX1STEX       Address of location of the first
                                            exposure block.
    000C   12 Signed       4 *              Reserved for IBM use.
    0010   16 Bitstring   16 MEXEXPBK (0)   Address of the first exposure
                                            block.
    0010   16 Address      4 *              Place for exposure block address.
              00000004       MEXENTLN       *-MEXEXPBK Length of an entry.
    0014   20 Address      4 MEXNXTEX (3)   Place for three exposure block
                                            addresses.
              00000004       MEXEXPEC       L'MEXEXPBK/MEXENTLN Count of
                                            entries in the exposure block
                                            field MEXEXPBK.
              00000020       MEXLEN         *-MEXBK
              00000004       MEXSIZE        (MEXLEN+7)/8 Number of
                                            doublewords.
         Use this to DSECT the read and write areas MEXFRDEX, MEXLRDEX, MEXCRDIT
         and MEXFWREX, MEXLWREX, MEXCWRIT.

    MEXENTRY DSECT

    Hex   Dec Type/Val   Lng Label (dup)    Comments
    ---- ---- --------- ---- -------------- --------
    0000    0 Structure      MEXENTRY       MULTIPLE EXPOSURE BLOCK
    0000    0 Bitstring    1 MEXFIRST       First available write exposures
    0001    1 Bitstring    1 MEXLAST        Last write exposure
    0002    2 Bitstring    1 MEXCURR        Current available write exposure

    MEXBK Storage Layout

    *** MEXBK - MULTIPLE EXPOSURE BLOCK
    *
    *     +------+------+------+------+------+------+------+------+
    *   0 |:CTEXP|//////|:FRDEX|:LRDEX|:CREAD|:FWREX|:LWREX|:CWRIT|
    *     +------+------+------+------+------+------+------+------+
    *   8 |         MEX1STEX          |///////////////////////////|
    *     +---------------------------+---------------------------+
    *  10 |///////////////////////////|         MEXNXTEX          |
    *     +---------------------------+                           |
    *     |                                                       |
    *     +-------------------------------------------------------+
    *  20
    *
    *** MEXBK - MULTIPLE EXPOSURE BLOCK

    *** MEXENTRY - MULTIPLE EXPOSURE BLOCK
    *
    *     +------+------+------+
    *   0 |:FIRST|:LAST |:CURR | 3
    *     +------+------+------+
    *
    *** MEXENTRY - MULTIPLE EXPOSURE BLOCK

    MEXBK Cross Reference

    Symbol         Dspl Value
    -------------- ---- -----
    MEXCREAD       0004
    MEXCTEXP       0000
    MEXCURR        0002
    MEXCWRIT       0007
    MEXENTLN       0010 00000004
    MEXEXPBK       0010
    MEXEXPEC       0014 00000004
    MEXFIRST       0000
    MEXFRDEX       0002
    MEXFWREX       0005
    MEXLAST        0001
    MEXLEN         0014 00000020
    MEXLRDEX       0003
    MEXLWREX       0006
    MEXNXTEX       0014
    MEXRDWRI       0002
    MEXSIZE        0014 00000004
    MEX1STEX       0008

    This information is
    based on z/VM V4R3.0.
    Last updated on 30 Apr 2002 at 16:56:42 EDT.

    Copyright IBM Corporation, 1990, 2002