Non-SNA 3270 screen-size and model information

Model information applies to VTAM® 3270 Record-Mode devices (non-SNA 3270s).

To determine the model or screen-size for ETO terminals IMS uses the following algorithm:

Procedure

  1. Screen-size is established based on the model specification in the VTAM PSERVIC field. IMS determines the model by checking the screen-size control byte in the VTAM PSERVIC field for 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. Device type and screen-size are determined from the model value.
  2. Screen-size is established based on the screen-size specifications in the VTAM PSERVIC field. A value of X'7E' in the screen-size control byte causes the default screen size in the VTAM PSERVIC field to be used. A X'7F' causes the alternate screen-size to be used first in searching 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. Device type and screen-size are implied by the model value.
  3. If the screen-size control byte is X'00', the default and alternate screen-size specifications in the VTAM PSERVIC field 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 found, the logon is rejected. Device type and screen-size are implied by the model value.
  4. If no model information and screen-size are specified in the VTAM PSERVIC field, IMS uses the CINIT's model byte. Model type is established by the VTAM definition statement FEATUR2. The model information applies only if the screen-size control byte is X'00' and if the screen-size is also X'00'. This applies to printers and displays. X'00' is the default and corresponds to a model 1. X'01' corresponds to a model 2. Device type and screen-size are implied by the model value.
  5. The screen-size is used to determine the type of write command used. If the screen-size is equal to 960 or greater than 1920, IMS uses erase write alternate (EWA). If the screen-size is less than or equal to 1920 and not equal to 960, IMS uses erase write (EW). The device type and screen size are determined from the model value.

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. 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. Device type and screen-size are determined from the model value.

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. Device type and screen-size are implied by the model value.