Application programming for the CICS 3270 bridge
Application programming for the CICS 3270 bridge is usually more complex than application programming for the DPL bridge for these reasons:
- The bridge emulates all the functions of the CICS terminal API, including minimum function BMS.
- The bridge application needs to be aware of the internal logic and flow of control in the CICS transaction that is being run, and it must interpret and respond to vectors that it receives in outbound messages.
- If a transaction uses BMS maps, the bridge application might not have access to the copybooks created during map assembly to help interpret data in the vectors. In this case, the data must be analyzed indirectly through the use of an application data structure (ADS) descriptor.
If you are unfamiliar with the terminology used for describing application data structures, refer to the section Application data structure terminology.
Ensure that every inbound message that is sent to the CICS 3270 Bridge includes a vector structure after the CIH, except when you start a transaction with no data.
The vector structure definitions are available in C-language header file dfhbrmqh.h and COBOL copybook DFHBRMQO. Include these in any application that uses the bridge. These members are only provided with CICS Transaction Server on z/OS™. If you want to create your application on another platform, copy them to that environment.
All the vectors have a common header, but their structures differ. Details of the structures are given in the CICS Internet and External Interfaces Guide for CICS V2.2, or the CICS External Interfaces Guide for CICS V2.3. Refer to these books when you are developing your bridge applications.
Obtain a copy of CICS SupportPac™ CA1E "CICS Bridge Passthrough" as an aid to analyzing the logic of your existing CICS transactions, and to help plan your WebSphere MQ CICS 3270 bridge applications. You might be able to use the SupportPac to test application code. It also enables you to display and capture the inbound and outbound data flows, to study how messages must be structured, and what values to insert into fields in the MQCIH and the vectors.
This example illustrates how you might write applications for the CICS 3270 bridge; it shows how to invoke a transaction that would normally be started by entering its identifier and some command line arguments at a CICS terminal:
Parent topic:
Using CICS transactions with the bridge
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