DFHTCT logical device codes: z/OS Communications Server non-3270

Certain types of logical unit may be used to gain access to more than one resource within a subsystem. For example, a card punch device may be attached to a 3770 logical unit: the CICS® application program can direct punch output, through BMS, via the 3770 to the card punch device. The facility provided by CICS to permit communication to devices within logical units of this type is the logical device code (LDC).

Certain types of logical unit may be used to gain access to more than one resource within a subsystem. For example, a card punch device may be attached to a 3770 logical unit: the CICS application program can direct punch output, through BMS, via the 3770 to the card punch device. The facility provided by CICS to permit communication to devices within logical units of this type is the logical device code (LDC).

Although these are z/OS® Communications Server units, they require macro definition, unlike other z/OS Communications Server devices.

The logical units that support LDCs are:
  • 3601 logical unit
  • 3770 batch logical unit
  • 3770 batch data interchange logical unit
  • 3790 batch data interchange logical unit
  • LUTYPE 4 logical unit

To reference such a device in a CICS application program, or in the CMSG transaction for message switching, you specify an LDC mnemonic which CICS translates into a numeric LDC value. When CICS sends an output data stream to the logical unit, it includes the LDC value in the function management header (FMH). When the logical unit receives the data stream, it uses the LDC value to determine which component is to receive the output, or to perform some standard action.

Each LDC mnemonic to be referenced must be defined in the TCT, optionally with its associated LDC value and certain device characteristics for use by BMS functions. Such LDC information is contained in either the system LDC table, or in an extended local LDC list. You code the following DFHTCT macros to specify the system LDC table or an extended local LDC list:
  • Code DFHTCT TYPE=LDC macro(s) to generate entries in the system LDC table. You may generate certain default LDC entries provided by CICS. For example, 
    DFHTCT TYPE=LDC,LDC=SYSTEM

    generates the following entries in the system LDC table:

    Table 1. System LDC table entries
    LDC mnemonic LDC value Device Pagesize (row,column)
    DS 1 3604 Keyboard Display 6,40
    JP 2 3610 Document Printer 1,80
    PB 3 Passbook and Document Printer 1,40
    LP 4 3618 Administrative Line Printer 50,80
    MS 5 3604 Magnetic Stripe Encoder 1,40
    CO 0 Console medium or default print data set group  
    R1 32 Card input medium 1,80
    H1 32 Card output medium 1,80
    P1 48 Print medium or print data set group 50,80
    W1 128 Word processing medium 1 50,80
    W2 144 Word processing medium 2 50,80
    W3 160 Word processing medium 3 50,80
    W4 192 Word processing medium 4 50,80
    You may also define LDCs specifically to add LDC entries to the system LDC table. For example, 
       DFHTCT TYPE=LDC,
          LDC=XX,
          DVC=BLUPRT,
          PGESIZE=(12,80),
          PGESTAT=PAGE
   DFHTCT TYPE=LDC,
          LDC=YY,
          DVC=BLUPCH,
          PGESIZE=(1,80),
          PGESTAT=AUTOPAGE
    adds the following entries to the system LDC table:
    Table 2. System LDC table entries defined by LDCs
    LDC mnemonic LDC value Device Pagesize (row,column) PGESTAT
    XX 48 Batch LU printer 12,80 PAGE
    YY 32 Batch LU card output 1,80 AUTOPAGE
  • Instead of the system LDC table, you may code the following series of DFHTCT TYPE=LDC macros to create an extended local LDC list. Default entries may also be generated. For example, 
    LDC1  DFHTCT TYPE=LDC,LOCAL=INITIAL
*  the next line generates default CO,R1,H1,P1 LDCs
   DFHTCT TYPE=LDC,LDC=BCHLU
   DFHTCT TYPE=LDC,DVC=BLUPRT,LDC=AA,
          PGESIZE=(6,30)
   DFHTCT TYPE=LDC,DVC=BLUPCH,LDC=BB,
          PGESIZE=(1,80)
   DFHTCT TYPE=LDC,DVC=BLUCON,LDC=CC,
          PGESIZE=(1,132)
   DFHTCT TYPE=LDC,LOCAL=FINAL
    generates an extended local LDC list named LDC1 containing the following entries:
    Table 3. Extended local LDC list entries
    LDC mnemonic LDC value Device Pagesize (row,column)
    CO 0 Console medium or default printer data set group  
    R1 32 Card input medium 1,80
    H1 32 Card output medium 1,80
    P1 48 Print medium or print data set group 50,80
    AA 48 BLUPRT batch LU printer 6,30
    BB 32 BLUPCH batch LU card output 1,80
    CC 0 BLUCON batch LU console printer 1,132
When you are defining a logical unit in the TCT, you can specify its LDCs in either of two ways:
  1. Code a DFHTCT TYPE=LDCLIST macro to define a local list of LDC mnemonics (and optionally their LDC values); for example, 
    LDC2 DFHTCT TYPE=LDCLIST,
            LDC=(DS,JP,PB=5,LP,MS)
    In the DFHTCT TYPE=TERMINAL macro defining the logical unit, you specify in the LDC operand the name of the local list as defined by the DFHTCT TYPE=LDCLIST macro. For example: 
         DFHTCT TYPE=TERMINAL,
            TRMTYPE=3600,
            LDC=LDC2, ...

    has associated the LDCs DS, JP, PB, LP, and MS with the 3601 logical unit that you are defining. The LDC values either may be specified in the local list, or are obtained from the system LDC table. If BMS uses these LDC mnemonics, their page size and page status must also be available from the system LDC table.

    Note: A local list defined by a DFHTCT TYPE=LDCLIST macro may be shared by a number of 3601, LUTYPE 4 and batch logical units.
  2. In the DFHTCT TYPE=TERMINAL macro defining the logical unit, you specify in the LDC operand the name of an extended local LDC list. For example: 
    LDC1 DFHTCT TYPE=LDC,LOCAL=INITIAL
     DFHTCT TYPE=LDC,LDC=BCHLU
     DFHTCT TYPE=LDC,DVC=BLUPRT,LDC=AA,
            PGESIZE=(6,30)
     DFHTCT TYPE=LDC,DVC=BLUPCH,LDC=BB,
            PGESIZE=(1,80)
     DFHTCT TYPE=LDC,DVC=BLUCON,LDC=CC,
            PGESIZE=(1,132)
     DFHTCT TYPE=LDC,LOCAL=FINAL
     DFHTCT TYPE=TERMINAL,TRMTYPE=BCHLU,
            LDC=LDC1, ...

    has associated the LDCs CO, R1, H1, P1, AA, BB, and CC with the batch logical unit that you are defining. Their LDC values and device characteristics for BMS functions are described in the extended local LDC list, which is named LDC1.

When CICS requests an output or message switching operation using a particular LDC mnemonic for a logical unit, it tries to resolve the mnemonic from the list (whichever form) specified by the LDC operand of the DFHTCT TYPE=TERMINAL macro. If the LDC is not located in the local list or in the extended local list, the LDC specified is not valid for that terminal entry. In this case, X'00' is inserted in the logical device code portion of the FMH, and no destination name is inserted.

When a BMS function is requested for an LDC, and the LDC mnemonic is successfully resolved, the device characteristics (for example, device name and destination name) are accessed for the BMS function. If the LDC is in an extended local LDC list, these characteristics lie in the located extended local list entry. Otherwise, the system LDC table is searched for the LDC and the associated device characteristics.