Video IO for Text

1
Video I/O for Text

• Write directly to video memory
• High speed, medium compatibility
• (buffer address varies depending on type of
• Video display and manufacturer)
• Output cannot be replaced unless MRS monitors
  access to video buffer and reroutes it
• BIOS-level INT (Int 10)
• Medium speed, high compatibility
• Output cannot be redirected unless ISR replaced
• DOS-level INT (Int 21)
• Low speed
• Output can be easily redirected to other devices

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Basic Text Screen
3
Text Modes (can only display characters from the
IBM extended Character set)
4
Graphics Mode-(can draw any combination of
pixels(dots)
5
BIOS

• Basic Input Output Service a set of X86
  routines stored in ROM that can be used by any
  operating system for low level I/O to various
  devices.
• Int 10h Video Services
• Int 16h Keyboard Services
• Int 17h Printer Services
• Int 33h - Mouse Services

6
Bios Interrupt 10h Video Services
7
Lab 7A Positioning the Cursor

• Irvine Library Function Clrscr
• Dos Int 21h, Function 7 get char with no echo
• w- move up - a move left
• s move down - d move right
• Procedure Setcur uses BIOS int 10h, function
  2 to set cursor position.

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Monochrome Attributes
9
Color Attributes foreground chars
background screen behind chars b7
b0
10
BIOS Interrupt 10h- Video Services
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Lab 7B Character Attributes

• Procedure setcur positions cursor
• Procedure wchar writes character with attribute
  at current cursor position (will have to
  increment column)

12
Random Number Generation

• Irvine Library Functions
• Randomize Re-seeds the random number generator.
  Current time value is seed value. No input or
  output required. Only needs to be called once at
  the beginning of a program.
• Random_Range Returns a pseudo-random 32-bit
  integer between 0 and n. Input EAX n.

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Lab 7C Pseudo-Random Numbers Delay

• Randomize and Random-Range used for random number
  generation. EAX 10 to produce the values 0-9.
  To display ASCII value, 30h added to returned
  value.
• Procedure mywait waits the number of
  milliseconds in CX.

14
Mywait Procedure

• Uses 64-bit timer
• Timer accessed through timget procedure
• Uses rdtsc (read time stamp counter)
• Windows 95 and some 98 versions have problems
  with the timget procedure
• Inner loop of mywait waits number of timeticks
  equivalent to 1 millisecond (TICS_MS
  CLKFREQ1000)
• Need to set CLKFREQ your PC clock frequency

15
CLKFREQ

• START-gtSearch-gtFind-gtFILES/Folders
• Find msinfo32.exe
• Programs-gtAccessories-gtSystem Tools-gtSystemInfo
• System Summary
• Reboot PC watch BIOS screen information