### 18.2.6. Structure of the User Junction Box Routines

Junction box routines have a fixed argument list that contains only the global stacks; no further arguments can be passed to them. Therefore, the argument and unit information that is required for user CEL functions is not required for junction box routines. Junction box routines always work in base units, as specified in the `FLOW > SOLUTION UNITS` section of a CCL file or on the Solution Units form in CFX-Pre. For details, see Setting the Solution Units in the CFX-Pre User's Guide.

MMS (Memory Management System) calls can be used in junction box routines to access CFX-Solver data. For details, see CFX Memory Management System (MMS).

A template junction box routine, jcb_template.F, is in `CFXROOT`/examples/.

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