Ch 16: Interfacing Assembly with C/C++

Why did IBM introduce extended ASCII semi-graphics characters (codes 128 to 255) when the IBM PC was launched?

Explain how the contiguous arrangement of ASCII character codes simplifies case conversion (uppercase/lowercase) and digit-to-ASCII conversion in 8088 assembly language.

add al, 0x30
sub bl, 0x20

Describe how the CPU accesses Video Memory (VGA Text Mode RAM) via Memory-Mapped I/O, and explain how screen manipulation works at the hardware memory bus level.

mov ax, 0xb800
mov es, ax

In standard 80x25 text mode, how is a 2D screen mapped into 1D linear video memory? State the memory size per character cell and give the formula for calculating the byte offset of a character at row R and column C.

; Offset = (row * 80 + col) * 2

Summarize the three core principles of VGA text mode display memory architecture in IBM PC systems.

Why was the physical memory address for color text mode display memory standardized at 0xB8000 (segment base 0xB800), and how does the CPU load segment registers to access it?

mov ax, 0xb800
mov es, ax
mov byte [es:0], 'A'

Explain the purpose and structure of the Video Attribute Byte in VGA 80x25 text mode display memory.

mov byte [es:1], 0x07

Explain the detailed bit layout of the 8-bit Video Attribute Byte in VGA 80x25 text mode, detailing how foreground colors (16 possibilities), background colors (8 possibilities), and character blinking are controlled.

mov byte [es:1], 0b10000111