Accessing programs that use MFS

If a program that uses MFS program is sensitive to the MFS MODname, MFS must be used when input is received from an ISC session.

Your program is sensitive, for example, if the program tests the MODname in the IOPCB as part of its logic, or uses ISRT calls to the IOPCB that include a MODname as part of the call.

If your program is sensitive to cursor position, it cannot be used to receive ISC session input. An ISC LTERM is not a hardware device and, as a result, cursor position has no meaning.

For output, MFS provides support for attribute and extended attribute bytes.

ISC supports the system control area (SCA) and default system control area (DSCA) in the following manner. All functions allowed for the 3270 display can be specified by the application program in a message field (MFLD) defined as an SCA. A device field (DFLD statement) can be defined as an SCA in the device output format (DOF). For ISC subsystems, MFS does not interpret the SCA specifications; it merely relays them in the user-defined device field SCA that it sends to the remote program or ISC subsystem. The MFS-supported SCA, or DSCA, for ISC session output can be used by the receiving application program to intelligently handle a terminal device attached to its subsystem.

If your application program is not sensitive to MFS formatting, it is possible for an ISC-connected subsystem to send an input data stream to your program without invoking MFS. To accomplish this, the sending subsystem must construct an input data stream that is exactly the same as your program's I/O area. This bypassing of MFS would result in a reduction of the processor overhead associated with MFS. Bear in mind that bypassing MFS in this manner can result in the transmission of inefficient data streams from the sending subsystem and also makes the sending subsystem sensitive to changes in your program's I/O area.

It is probably easiest, from an implementation point of view, to use MFS with ISC when MFS is already used for input to your program. In this case, you simply create ISC (DPM-Bn) device input formats (DIF) and DOFs.