When you build a BMS logical message for a terminal for which partitions have been established, you can direct the pages of the message to multiple partitions. You can even send text output to some partitions and mapped output to others, provided you do not mix them in the same partition. (This is an exception to the normal rule against mixing text and mapped output in a logical message.)
When the output is displayed, the first page for each partition is displayed initially. The pages are numbered by partition, and CSPG commands that the operator enters into a particular partition apply only to that partition, with the exception of the page purge command. The purge command deletes the entire logical message from all partitions.
On each BMS SEND that contributes to the message, you specify the partition to which the output goes. If you are not using ACCUM, BMS builds a page for that partition. If you are using ACCUM, BMS puts the output on the current page for that partition. Page overflows therefore occur by partition. If you are intercepting overflows and are not sure in which partition the overflow occurred, you can use the PARTNPAGE option of the ASSIGN command to find out.
The bookkeeping required to handle page overflow when you are distributing pages among partitions is analogous to that required in a routing environment (see Routing and page overflow). In particular, you need to ensure that you finish overflow processing for one partition before doing anything that might cause overflow in another. Failure to do so can cause program loops as well as incorrect output.
You cannot route a logical message written to multiple partitions. BMS ignores the OUTPARTN and ACTPARTN options on BMS SEND commands in a routing environment.
You can route an ordinary message to a terminal that supports partitions, but BMS builds the message and the CSPG transaction displays it using the terminal in base (unpartitioned) state.
You also cannot use partitions and logical device codes together (LDCs are described in Logical device components). In addition, you cannot use partitions in combination with GDDM®, although you can use partitions with outboard formats (see Outboard formatting).
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