6530 Programmer's Guide

Block Mode Operation
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6530 Programmer’s Guide
Once set, the display page continues to be displayed until another Esc ;
sequence is issued. The default page used immediately after entering
block mode is page 1.
Displaying page 0 (20H) locks the keyboard and displays a blank screen.
This is useful for preventing video flash, which occurs if your application
simultaneously displays and writes video attributes to the same page. For
example, your application can display page 0 while it is writing to page
1.
Select Page (Esc :)
The Esc : sequence selects the memory page accessed by your
application program. The escape code is followed by an ASCII character
whose code, offset by 20H, specifies the page number. The valid range
for this character code is 21H (for page l) through the maximum number
of available pages. Character codes outside of this range cause the escape
sequence to be ignored, and the currently selected page remains
unchanged.
Once a page is selected, it remains selected until another Esc : sequence
is issued. The default page number used immediately after entering block
mode is page 1.
Set Max Page Number (Esc p)
The Esc p sequence changes the default value for the maximum number
of pages allocated. Typically, this escape sequence is used to increase the
amount of memory available for defining fields in protect submode. The
Esc p is followed by an ASCII character whose code, offset by 30H,
specifies the maximum number of pages to be allocated. For example,
the character 7 causes the 6530 to allocate memory for up to 7 pages.
The default values and the absolute maximum number of available pages
depends on the screen format selected. You can use the Esc ^ (read
terminal status) sequence to determine the number of pages available.
Specifying a value greater than the absolute results in a default to the
absolute maximum.
The new value set for the maximum page number does not take effect
until a switch to a submode occurs or the screen format is changed.