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 VTAM® units, they require macro definition, unlike other VTAM devices.
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.
DFHTCT TYPE=LDC,LDC=SYSTEM
generates the following entries in the system LDC table:
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 |
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: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 |
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:
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 |
LDC2 DFHTCT TYPE=LDCLIST,
LDC=(DS,JP,PB=5,LP,MS)
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.
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.