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assembly language step by step programming with dos and linux PHẦN 8

Những giá trị này được chiết xuất nên được các biến thông thường trong các phân đoạn dữ liệu, dễ dàng truy cập mà không cần tìm kiếm bàn thêm. Các biến này được xác định với nhau, như một khối, với ý kiến, giải thích làm thế nào họ có liên quan: | subtables give you just about everything you d really need to know about a given display adapter to do useful work with it. When your assembly-language program begins executing it should inspect such a table and extract the values pertinent to the currently installed display adapter. These extracted values should be ordinary variables in the data segment easily accessible without further table searching. These variables should be defined together as a block with comments explaining how they are related i DISPLAY _ _ a. a - a a a - _ _ a .Bl a a a a . a a a T a rnvirn INFORMATION VARIABLES The following block of variables all relate to the video Ị system and arc Initialized by ttiE Vid heck procedure Di splype 08 Q Code for display adapter type VidOrigin Dw Q Offset for FAR pointer to refresh buffer VidSegment Ok 0BOOOH Segment of installed display buffer Visible ỮB ao Number of columns on screen Vi s t bleY Ữ0 25 Number of lines on screen VIiflirfSi ze DW 4ŨŨO Default to 26 X BO X 2 char attribute FontSIzc DB 8 Either 8d 14h or Ĩ6 default to a SardName DW J NEAR pointer t.o name string of Installed board Í IflH - Z 0 4FH 79D Combined ũ-bỉiíd t.Y of 80 X SB screen Lft corner LRIY OH 1B4FH As the comments indicate a single procedure named VidChek reads values from the two-level lookup table VidInfoTbl and loads those values into the variables shown above. VidCheck is an interesting creature and demonstrates the way of dealing with two-level tables. Read it over VtdCheck Identifies display board display parameters Last update 3 16 89 1 entry point VidCheck Caller passes no parameters. VTdCheck identifies the Installed display board by calling 01spID. t then calculates numerous display Information values 4-h1cti It then stores In the block of display Information variables in the data Segment VidCheck PROC Ỉ First task 1s to figure out which board is on the bus call Uisplti Ask 010 for adapter eod i returns in AL mow CIspType.AL Store display adapter code in DIspType .