6530 Programmer's Guide

Block Mode Operation
3-2
6530 Programmer’s Guide
Each field is defined by a start-field (GS control character or Esc [ )
sequence. The sequence includes attribute characters that assign both
video and data attributes to that field. The following shows an example
of two adjacent fields on a page:
The invisible (blank) video attribute character takes up a displayed
position on the page, and its location is set to the current buffer address
for the selected page. This location is referred to as the start-field
address.
The data attributes for a field take effect one character position to the
right of the start-field address. This location is referred to as the first
position of the field or the beginning of the field. The data attributes are
stored in a data attribute table separate from the contents of the page.
The data attribute table contains one entry for each defined field; each
entry is associated with the video attribute character (start-field address)
for that field.
Once a field is defined, all subsequent positions on the page up to the
next start-field address have the same data attributes. A new field is
defined by changing the buffer address, then issuing another start-field
sequence. A new start-field sequence terminates the previous field as
well as starting the next field.
Your application program can change the video and data attributes of an
existing field by reissuing a start-field sequence. When the current buffer
address is equal to the start-field address of an existing field, that field’s
attributes are modified; otherwise, a new field is created.
Using the set video attributes (Esc 6) sequence, you can also assign
different video attributes within an existing field without affecting the
data attributes. The Esc 6 video attribute character also takes up a
position on the page, but it does not define a start address for a new field.
Data attributes can only be assigned with a start-field sequence.
Field 1 (F1) Field 2 (F2)
Start-field address for F1
(video attribute character)
First position of F1
(data attributes take
First position of F2
(data attributes take
Start-field address for F2 (vide
o
attribute character)