Control blocks

BMS makes use of the following control blocks (see Figure 1):

DSECT	Function
DFHMAPDS	Defines a physical map. It contains overlays for map set data, map data, and field data. The physical map set is stored in the CICS® program library and requires a resource definition when loaded into main storage by BMS.
DFHMCAD	Defines a mapping control area (MCA). MCAs are used in DFHM32 and DFHML1 to merge (both) and sort (DFHML1 only) fields in different maps in the chain of map copies. The MCA contains field position, flags, and pointers to map and application data structure relating to this field.
DFHMCBDS	Defines the message control block (MCB). MCBs are built and referenced by DFHTPR. There is one MCB per level of page chaining. The MCBs are chained together, with the head of the chain anchored off the TCTTE BMS extension. The MCB contains a copy of the MCR, with additional working data.
DFHMCRDS	Defines the message control record (MCR). MCRs are held in CICS temporary storage. There is one MCR per BMS message in temporary storage. The MCR contains data such as the number of pages in this message, the list of target terminals for this message, data on which pages are for which LDCs or partitions, and so on. The MCR is written to temporary storage by DFHMCP. It is read and purged by DFHTPR, DFHTPS, and DFHTPQ.
DFHOSPWA	Defines the output services processor work area (OSPWA). This is the main BMS control block. For standard and full-function BMS, there is an OSPWA that is chained off the TCA and is built by DFHMCP on the first BMS command in a transaction. It contains a copy of the BMS TCA request bytes, together with the BMS status and working area. DFHTPR has its own private OSPWA. This overlays the TWA for DFHTPR unless SEND PAGE RETAIN is used. If SEND PAGE RETAIN is used, DFHTPR obtains an additional OSPWA, and chains the base OSPWA off the new OSPWA. This avoids DFHTPR damaging the base OSPWA. The OSPWA is deleted during task termination. A shorter version of the OSPWA is used by DFHMCPE (part of both the minimum-function BMS mapping control program DFHMCPE$ and also the BMS fast-path module DFHMCX). It is built in DFHMCPE∾€™s LIFO storage, and includes space for the request information from the TCA. The DFHMCPE OSPWA is defined within DFHMCPE.
DFHPGADS	Defines a page control area (PGA). DFHTPP builds a PGA at the end of the device data stream in the terminal input/output area (TIOA) (addressed as ADDR(TIOADBA) + TIOATDL) for the SET and PAGING disposition. The PGA contains the 3270 write control character (WCC), flags about the type of TC write required, and the extended features used in this page of data stream.
DFHPSDDS	Defines a physical partition set. The partition set is stored in the CICS program library and requires a resource definition when loaded into main storage by BMS.
DFHTTPDS	Defines the terminal type parameter (TTP). This contains information for a terminal type. Note that BMS builds pages on a TTP basis. For standard and full-function BMS, DFHRLR builds TTPs as follows: A "direct TTP" is built for the transaction terminal. If this supports partitions or LDCs, a further direct TTP is built for each referenced LDC or partition. This contains data for that LDC or partition. These direct TTPs are chained together, and the head of the chain is contained in the OSPWA. Direct TTPs are deleted by DFHMCP on a SEND PAGE, PURGE MESSAGE, or SEND PARTNSET command. If routing is in effect, there is a chain of routed TTPs, with one TTP per terminal type in the route list. Routed TTPs are deleted by DFHMCP on a SEND PAGE or PURGE MESSAGE command. Most of BMS uses the TTP rather than the TCTTE to determine terminal-related information.
TCTTETTE	The TCTTETTE DSECT in the DFHTCTZE macro defines the TCTTE BMS extension. It is chained off the TCTTE (TCTTETEA field).
DFHTPE	Defines the BMS partition extension. This is chained off the TCTTE BMS extension if the terminal supports partitions.

Diagram showing the control blocks associated wih basic mapping support (BMS) and the relationships between them. — Figure 1. Control blocks associated with basic mapping support (BMS)