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Method to Restore Value and Condition of Color-Look-Up-Table

IP.com Disclosure Number: IPCOM000114860D
Original Publication Date: 1995-Feb-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 95K

Publishing Venue

IBM

Related People

Hirano, Y: AUTHOR [+2]

Abstract

Disclosed is a programming method to save and restore the values of Color-Look-Up-Table (CLUT) and the condition of the pointer and the access mode (read or write) of Video Digital-to-Analog Converter (DAC) in VGA and compatible video adapters.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Method to Restore Value and Condition of Color-Look-Up-Table

      Disclosed is a programming method to save and restore the
values of Color-Look-Up-Table (CLUT) and the condition of the pointer
and the access mode (read or write) of Video Digital-to-Analog
Converter (DAC) in VGA and compatible video adapters.

      In VGA, a standard architecture of video controller for
portable computer, the software interface of video DAC is as shown in
Table 1.  This interface has the following limitations from the
system software.

o   both in read or write mode, the pointer to Red/Green/Blue is
    auto-increment and not readable.  Moreover it is lost if read or
    write address is overwritten before a cycle access to R/G/B is
    completed.
  o  in read mode, the address is not readable.
  o  in write mode, write data of incomplete cycle is(are) not
      readable.

      By the following method, the values of CLUT and the above
condition of DAC can be saved at any moment, and restored after any
modification or corruption, including power-on-reset of VGA.
  1.  Fig. 1 shows a general flow of save/restore.  According to the
       access mode at that time, which can be read from DAC State
       register (3C7h), save/restore procedure for each mode is used.
       The operation of application or OS software can be stopped and
       restarted again at any timing.
  2.  Fig. 2 shows the save/restore in read mode.
      a.  Read the data register (3C9h) for 256 x 3 times and save
the
           values as data set A, without accessing the read address
           register (3C7h).
      b.  Set the address register to '0' then read also for 256 x 3
           times and save the values to data set B.
      c.  Compare the two data sets and find a set of address and
           pointer which makes...