Defining device types

If the definitions are coded incorrectly, IMS chooses the wrong MFS format and device characteristics, possibly causing screen format errors.

IMS dynamic terminal control blocks are built from definitions in a combination of the following:
  • The logon descriptor
  • Information that VTAM® passes to IMS during logon
  • The MFS device characteristics table
VTAM passes the physical terminal characteristics to IMS. The following fields have information that IMS uses to determine device types:
  • LUTYPE field from the VTAM PSERVIC parameter of the VTAM MODEENT macro
  • TS profile from the TSPROF parameter of the VTAM MODEENT macro

Non-SNA 3270 printers and displays

The default descriptor names for non-SNA 3270 printers and displays are DFS327P and DFS3270.

Rules required for defining non-SNA 3270 devices are:
  • The TSPROF parameter of the VTAM MODEENT macro must be 2 or 3.
  • The PSERVIC parameter of the VTAM MODEENT macro must specify LU Type=0.
  • Byte 12 in the VTAM PSERVIC parameter must be modified so that it distinguishes a printer from a video. The following table shows the content that specifies each device type based on the bit location in byte 12:
    Table 1. Bits in byte 12 of the VTAM PSERVIC parameter
    Bits in byte 12 Content
    0-1 Device type:
    00
    Unspecified device type
    01
    Printer device
    10
    Display device
    11
    Display/printer device (3275)
    2-7 Reserved.

If you specify nothing (B'00'), the default is B'10', which is a display device. 1

Related reading: For more information on defining non-SNA 3270 devices, see z/OS® Communications Server: SNA Programming.

LU type-2 devices

The following is a list of rules required for defining SLU–2 devices:

  • The TSPROF parameter of the VTAM MODEENT macro must be 3.
  • The PSERVIC parameter of the VTAM MODEENT macro must specify LU Type=2.

Related reading: For more information on defining LU type–2 devices, see z/OS Communications Server: SNA Programming.

3275 devices

VTAM definitions alone cannot identify a 3275 device as it is logging on. Additional information (UNIT=3275) must be specified in a logon descriptor. Define this descriptor in the CINIT user data or in the Logon exit routine. The descriptor itself must be identified as a 3275 device type.

Static 3275 devices are defined in the IMS system definition as follows: 
TYPE     UNITYPE=3270 TERMINAL UNIT=3275,TYPE=3270-An,SIZE=(24x80),COMPT=PRT1
The 3275 has only one buffer. This forces the display and printer components to be the same model. The VTAM definitions for a dynamic 3275 as statically defined are: 
PSERVIC=X'000000000000185000007EC0'

NTO devices

The terminal must identify itself as an NTO device in one of the following ways:
  • LU presentation services profile in the BIND image must specify LU1.
  • When the LUTYPE is NTO, IMS uses the data stream compatibility byte to precisely define the specific NTO device type. If the LUTYPE specified is SLUTYPE1, the data stream compatibility byte is ignored. The terminal is assumed to be an actual SLUTYPE1 as defined on the logon descriptor.
  • Logon exit routine, if available, must accept the DFSNTO (default) logon descriptor or specify an NTO logon descriptor that is defined by your installation using the node name or LOGOND user data parameter.
  • The data stream compatibility byte in the CINIT specifies the device type. WTTY indicates a TTY NTO device. If nothing is specified, the device type is LUNS NTO.
1 B'00' means bits 0 and 1 equal 00. B'10' means bits 0 and 1 equal 10.