3270 field attributes

The field attributes byte holds the protection, modification, and display intensity attributes of a field. Your choices for each of these attributes are described here using the terms that BMS uses in defining formats. If you use terminal control commands, you need to set the corresponding bits in the attributes byte to reflect the value you choose.

See IBM 3270 Data Stream Programmers Reference for the bit assignments. See also Attribute value definitions: DFHBMSCA for help from CICS in this area.

Protection

There are four choices for the protection attribute, using up 2 bit positions in the attributes byte. They are:

Unprotected: The operator can enter any data character into an unprotected field.
Numeric-only: The effect of this designation depends on the keyboard type of the terminal. On a data entry keyboard, a numeric shift occurs, so that the operator can key numbers without shifting. On keyboards equipped with the “numeric lock” special feature, the keyboard locks if the operator uses any key except one of the digits 0 through 9, a period (decimal point), a dash (minus sign) or the DUP key. This prevents the operator from keying alphabetic data into the field, although the receiving program must still inspect the entry to ensure that it is a number of the form it expects. Without the numeric lock feature, numeric-only allows any data into the field.
Protected: The operator cannot key into a protected field. Attempting to do so locks the keyboard.
Autoskip: The operator cannot key into an autoskip field either, but the cursor behaves differently. (The cursor indicates the location of the next keystroke; for more information about this, see Input from a 3270 terminal .) Whenever the cursor is being advanced to a new field (either because the previous field filled or because a field advance key was used), the cursor skips over any autoskip fields in its path and goes to the first field that is either unprotected or numeric-only.

Modification

The second item of information in the field attributes byte occupies only a single bit, called the modified data tag or MDT . The MDT indicates whether the field has been modified or not. The hardware turns on this bit automatically whenever the operator changes the field contents. The MDT bit is important because, for the read command that CICS normally uses, it determines whether the field is included in the inbound data or not. If the bit is on (that is, the field was changed), the 3270 sends the field; if not, the field is not sent.

You can also turn on the MDT by program, when you send a field to the screen. Using this feature ensures that a field is returned on a read, even if the operator cannot or does not change it. The FRSET option on BMS SEND commands allows you to turn off the tags for all the fields on the screen by program; you cannot turn off individual tags by program. If you are using terminal control commands, you turn on a bit in the WCC to turn off an individual tag.

Intensity

The third characteristic stored in the attributes byte is the display intensity of the field. There are three mutually exclusive choices:

Normal intensity: The field is displayed at normal brightness for the device.
Bright: The field is displayed at higher than normal intensity, so that it appears highlighted.
Nondisplay: The field is not displayed at all. The field can contain data in the buffer, and the operator can key into it (provided it is not protected or autoskip), but the data is not visible on the screen.

2 bits are used for display intensity, which allows one more value to be expressed than the three listed previously. For terminals that have either of the associated special hardware features, these same 2 bits are used to determine whether a field is light-pen detectable or cursor selectable. Because there are only 2 bits, not all combinations of intensity and selectability are possible. The compromise is that bright fields are always detectable, nondisplay fields are never detectable, and normal intensity fields can be either. Cursor and pen-detectable fields contains more information about these features.

Base color

Some terminals support base color without, or in addition to, the extended colors included in the extended attributes. There is a mode switch on the front of such a terminal, allowing the operator to select base or default color. Default color shows characters in green unless field attributes specify bright intensity, in which case they are white. In base color mode, the protection and intensity bits are used in combination to select among four colors: normally white, red, blue, and green; the protection bits retain their protection functions as well as determining color. (If you use extended color, rather than base color, for 3270 terminals, note that you cannot specify "white" as a color. You need to specify "neutral", which is displayed as white on a terminal.)