3290 screen formatting

Screen division

The 3290 has a large screen, which allows the display of up to 62 rows by 160 columns for small character cells (6 × 12 pels), and up to 50 rows by 106 columns for large character cells (9 × 15 pels).

The 3290 screen can be divided into several areas, each of which interacts independently with the operator. This can be done in two ways:

• By dividing the screen into separate LUs
• By dividing a logical unit into separate partitions

In the first case, the 3290 terminal and its screen can be defined as up to four separate LUs. Each LU is independent of the others, and is defined to IMS as a separate terminal with its own address. This support is transparent to IMS. Defining multiple LUs is useful if the IMS application calls for more than one input or output message (or both) to be concurrently active between the 3290 terminal and IMS. For each logical unit, however, only one input or output message can be active.

In addition, with software partitioning, each logical unit can be divided into as many as 16 partitions. Each application message can specify a set of partitions, and each logical page of the message is associated with a particular partition of the partition set. Software partitioning is useful if:

• The operator needs to view more than one logical page at a time.
• One partition is needed to view an output page and another to input data.
• A partition is to be defined to receive IMS system error messages while the logical unit is in formatted mode. This function could be used in place of the current MFS SYSMSG field support.
• Scrolling is desired. Scrolling moves data up and down in the partition viewport. It can be defined only for a 3290 in partitioned mode. With explicit partition scrolling, you can define MFS pages for a presentation space larger than the viewport on the physical screen. This reduces the number of interactions between IMS and the terminal that must occur to display the message.

The 3290 allows a maximum of 16 partitions per physical device. Also, each LU defined in partitioned state must have available to it a minimum of 8 partitions, no matter how many partitions are actually defined for it. Thus, if one LU is defined with 9 partitions, no other LU can be in partitioned state, because there are only 7 partitions left for the physical device. Consequently, no more than 2 LUs (of the maximum 4 allowed) can be in partitioned state.

The following considerations also apply to defining partitions:

• Partitions must be rectangular.
• A single input message is constructed from one physical page of a single partition unless Multiple Physical Page Input is used. If it is used, then multiple physical pages for a single input message must come from a single partition.
• If the current PDB does not define a partition for system messages, and if the DOF does not define a system message field, then a system message destroys the current partitioned format mode and the 3290 (or the particular LU in question) returns to standard format mode.

Terminal states and modes

The 3290 as a single LU, or any of the LUs into which it has been divided, can be in terminal base state or terminal formatted state.

In terminal base state, the 3290 operates in the same way as any other currently supported SLU 2 node when it is initially connected to IMS or when the clear key has been pressed. In this state, input messages to IMS are edited with basic edit, and output messages without an associated MOD are formatted using the default MFS MOD.

In terminal formatted state, the 3290 can be in:

• Standard format mode
• Partitioned format mode

The choice of format mode is made dynamically at the time of message output. The output message is associated with a MOD, which in turn names a DOF. The specifications in the DOF determine the 3290 format mode:

• The 3290 is in standard format mode if the DOF does not name a partition descriptor block (PDB). The terminal is then formatted and operated as an ordinary SLU 2 node.
• The 3290 is in partitioned format mode if the DOF names a partition descriptor block (PDB).

Partition set initialization, paging, and activation

If the 3290 (or any of the LUs into which it can be divided) is in partitioned format mode, there are various ways in which:

• The partitions are initialized with one or more logical pages from the output message.
• The operator subsequently controls the flow of logical pages to the partitions.
• One particular partition becomes the active partition.

Initialization and operator-controlled paging are determined by selecting one of the three options. The option is specified by the PAGINGOP operand of the PDB. According to the selected option, initialization can consist of:

1. The message's first logical page going to the appropriate partition
2. The message's initial logical pages going to their appropriate partitions until the second logical page of any partition is reached
3. Each partition receiving its first appropriate logical page

The option also determines whether operator-controlled paging is affected, depending on which partition is active.

When the 3290 enters partitioned format mode, one particular partition is the active partition. This is determined in one of two ways:

• Logical pages are routed to their partitions using DPAGE statements. An ACTVPID operand might have been specified on one of the DPAGEs that points to an initialized partition. The ACTVPID allows the application program to declare which partition is the active partition.
• If no ACTVPID keywords are encountered, the active partition is the partition defined by the first PD statement in the PDB.

The active partition can be a partition that has not initially received any data.