LU2 screen-size and model information

Screen-size and model information applies to LU type–2 devices.

The following is an algorithm IMS uses to determine the model or screen size for ETO terminals:

Procedure

  1. Screen-size is established based on the model specification in the VTAM® PSERVIC. IMS determines the model by checking the screen-size control byte in the VTAM PSERVIC field for an X'01', X'02', or X'03'. The model is established accordingly. Screen-size specifications are ignored when the model is specified. X'01' represents a model 1 with a 12x40 screen-size, and X'02' and X'03' represent a model 2 with a 24x80 screen-size. If the model is specified, the MFS device characteristics table is not searched for MFS device information. The features are obtained from the logon descriptor.
  2. Screen-size is established based on the screen-size specifications in the VTAM PSERVIC. A value of X'7E' in the screen-size control byte causes the default screen size in the VTAM PSERVIC to be used. A X'7F' causes the alternate screen-size to be used first to search the MFS device characteristics table. If no match is found, the default screen-size is used to search; the first match is the screen-size. If no match is found, message DFS3646I is sent to the operator.
  3. If the screen-size control byte is X'00', the default and alternate screen-size specifications in the VTAM PSERVIC are used to search the MFS device characteristics table for MFS device information. If a match is made on the default size, the default is used. If a match is made on the alternate size, the alternate is used. If no match is made, the logon is rejected.
  4. If the screen-size control byte is X'00' and no screen-size is specified, the device is defaulted to a model 2 device, and the screen-size is established (24x80).
  5. The screen-size is established in the BIND parameter in the default screen-size field. The erase write (EW) command is always used.

If you want to override the model value, use the Logon exit routine (DFSLGNX0). Valid values are X'01' and X'02', corresponding to model 1 and model 2 in the logon descriptor. Screen-size and model specifications in the VTAM PSERVIC are ignored. Model=X'01' represents a 12x40 screen-size. Model=X'02' represents a 24x80 screen-size. The MFS device characteristics table is not searched for MFS device information. The features are obtained from the logon descriptor.

If you want to override the screen-size value, use the Logon exit routine, DFSLGNX0. Be aware that if you override the model, the screen-size override is ignored. The features from the logon descriptor and the screen-size are used to search the MFS device characteristics table for the MFS device information.