The connection between z/OS Connect and CICS is an IPIC connection. The CICS application that is being invoked must be a LINKable program -- using only the DPL subset of the CICS programming interface. Your API implementation can send either a Commarea or a Channel with Container(s) depending on which the CICS program is expecting.
If you have screen-based applications (aka transactions which run at a 3270 terminal, you need an intermediary. This can be a CICS facility using either FEPI or the 3270 Bridge. Your FEPI or Bridge program would be a LINKable program which then converses with the original 3270-based program. Or, you can use HATS to create a REST object which can be invoked via the z/OS Connect REST interface. I can't remember whether the API 3 environment supplies the REST interface or if you'd have to use an API 2 server with HATS.
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Leigh Compton
Consulting IT Specialist - CICS and Enterprise Integration
IBM
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