6530 Programmer's Guide

Block Mode Operation
6530 Programmer’s Guide 3-3
The number of fields that can be defined depends on the size of the data
attribute table. During block mode initialization, display memory is
allocated a default maximum number of pages. The default varies with
the 6530 and selected screen format. The rest of display memory is then
allocated to the data attribute table for defining fields. The read terminal
status (Esc ^) sequence returns the maximum number of pages available
as well as the average number of fields that can be defined for each page.
You can increase the amount of memory available for the data attribute
table by decreasing the maximum number of pages allocated (with the
Esc p sequence).
The data attribute character defines a field as either protected or
unprotected. The protected attribute, when set, always takes precedence
over the other data attributes for that field. Thus, when a field is defined
as protected, any data attributes that would apply to unprotected fields are
ignored. Unprotected fields can be modified from the keyboard as well as
from the application. Protected fields cannot be modified from the
keyboard, and the cursor cannot be positioned into these areas. However,
your application program can write into both protected and unprotected
fields.
Upon entering protect submode, all pages are cleared to blanks. Initially,
each page is defined as having one field, whose start-field address is
row l, column 1. This is called the default field and is defined as a
protected field. You can redefine the default field and/or define
subsequent fields in any order. The start-field address (video attribute
character) of each defined field is always protected, regardless of whether
the field is protected or unprotected. Thus, there is always at least one
protected blank between fields; and row l, column 1 is always a protected
position.
In addition to the protected/unprotected attribute, you can assign other
data attributes to a field, as described in the following paragraphs.
Modified Data Tags Each field, whether defined as unprotected or protected, has a modified
data tag (MDT). During certain read operations (Esc = and Esc - J
sequences), the 6530 transmits only those fields whose MDT is set;
transmission of all other fields is suppressed.
The MDT for an unprotected field is set by the terminal whenever the
user modifies the contents of that field, either by entering data or by
performing an edit operation (such as Erase Line) that effects the field’s
contents. Your application can reset the MDTs for all unprotected fields
by issuing a reset modified data tags (Esc >) sequence.