Outbound data stream example

The outbound data stream example shows the data stream required to paint a particular 3270 screen, to reinforce the explanation of how the data stream is built.

Figure 1 shows an example screen that is part of an application that tracks cars used by the employees at a work site, and is used to record a new car. The only inputs are the employee identification number, the license plate (tag) number, and, if the car is from out-of-state, the licensing state.
Figure 1. Example of a data-entry screen
 Car Record
						Employee No: ______ Tag No: ________ State: __
Note: This is an unrealistically simple screen, designed to keep the explanation manageably short. It does not conform to accepted standards of screen design, and you should not use it as a model.
There are eight fields on this screen:
  1. Screen title, “Car Record”, on line 1, column 26
  2. Label field, “Employee No:” (line 3, column 1), indicating what the operator is to enter into the next field
  3. An input field for the employee number (line 3, column 14), 6 positions long
  4. Label field, Tag. No:, at line 3, column 21
  5. An input field (tag number) at line 3, column 31, 8 positions long
  6. Label field, State:, at line 3, column 40
  7. An input field (state), at line 3, column 49, 2 positions long
  8. A field to mark the end of the previous (state) input field, at line 3, column 52

Table 1 shows the outbound data stream:

Table 1. 3270 output data stream
Bytes Contents Notes
1 X'F5' The 3270 command that starts the data stream, in this case erase/write.
2 X'C2' WCC; this value unlocks the keyboard, but does not sound the alarm or reset the MDTs.
3 X'11' SBA order to position first field at …
4-5 X'40D6' Address of line 1, column 23 on 24 by 80 screen, using 12 bit addressing.
6 X'1D' SF order to begin first field definition.
7 X'F8' Field attributes byte; this combination indicates a field which is autoskip and bright, with the MDT initially off.
8-17 'Car record' Display contents of the field.
18-20 X'11C260' SBA sequence to reset the current buffer position to line 3, column 1 for second field.
21 X'1D' SF order for second field.
22 X'F0' Field attributes byte: autoskip, normal intensity, MDT off.
23-34 'Employee No:' Display contents of field.
35 X'29' SFE order to start fourth field. SFE is required, instead of SF, because you need to specify extended attributes. This field starts immediately after the previous one ended, so you do not have to precede it with an SBA sequence.
36 X'02' Count of attribute types that are specified (two here: field outlining and field attributes).
37 X'41' Code indicating attribute type of extended highlighting.
38 X'F4' Extended highlighting value indicating underscoring.
39 X'C0' Code indicating attribute type of field attributes.
40 X'50' Field attributes value for numeric-only, normal intensity, MDT off. Any initial data for this field would appear next, but there is none.
41 X'13' Insert cursor (IC) order, which tells the 3270 to place the cursor at the current buffer position. We want it at the start of the first field which the operator has to enter data, which is the current buffer position.
42-44 X'11C2F4' SBA sequence to position to line 3, column 21, to leave the six positions required for an employee number. The beginning of the Tag No label field marks the end of the employee number input field, so that the user is aware immediately if they try to key too long a number.
45 X'1D' SF order to start field.
46 X'F0' Field attributes byte: autoskip, normal intensity, MDT off.
47-55 ' Tag No:' Display data. We attach two leading blanks to the label for more space between the fields. (We could have used a separate field, but this is easier for only a few characters.)
56 X'29' SFE (the next field is another input field, where we want field outlining, so we use SFE again).
57 X'02' Count of attribute types.
58-59 X'41F4' Code for extended highlighting with value of underscoring.
60-61 X'C040' Code for field attributes and attributes of unprotected, normal intensity, MDT off.
62-64 X'11C3C7' SBA sequence to reposition to line 3, column 40, leaving eight positions for the tag.
65 X'1D' SF to start field.
66 X'F0' Field attributes byte: autoskip, normal intensity, MDT off.
67-74 ' State:' Field data (two leading blanks again for spacing).
75-80 X'290241F4C040' SFE order and attribute specifications for state input field (attributes are identical to those for tag input field).
81-82 X'0000' The (initial) contents of the state field. We could have omitted this value as we did for other input fields, but we would need an SBA sequence to move the current buffer position to the end of the field, and this is shorter.
83 X'1D' SF. The last field indicates the end of the previous one, so that the user does not attempt to key more than two characters for the state code. It has no initial data, just an attributes byte. This field is sometimes called a “stopper” field.
84 X'F0' Field attributes byte: autoskip, normal intensity, MDT off.
Note: If you use terminal control commands and build your own data stream, the data you provide in the FROM parameter of your SEND command starts at byte 3 in the table; CICS® supplies the write command and the WCC from options on your SEND command.