INTRODUCTsedfasdIONer
programmablesdf devicefa and flat modes of operation
2-1 INTERNAL MIaasd
The Programming Modelfa
program visible
program invisibleqs
Multipurpose Rsdfegsdfisterass
RAX – 64-bit register(RAX), 32-bit(accumulator)(EAX), 16-bit(AX), and two
8-asdfbit registers (AsdH and AL)
RBX – RBX, EBX, BX, BH, BL. – BX register (base index)
RaCX, as RCX, ECasdX, CdfX, CH, or CL. (count)
RDsdfX, asdfasdfas RDXasdfaasdfsdf, EDX, DX, asdfaDH, or DL. (data)
RBP, as RBP, EBP,fa or BP. (Base Pointer)
RDfaI addressable as RDI, dfaEDI, or DI. (destination index)
RSI used as RSI, ESI, or SI. (Source Index)
R8 asd– R15 foundsdf in the fasdPentium 4 and Core2 if 64-bit extensions
are enabled.
Special-Purpose Registeasdfrs
RIP,f RSP, and RFLAGS
RIP defined as Register ifaasdnstruction pointer.
RSP dasdefined as Registerf stack pointer
RasdfFLAGS
List of Each Flag bit, with asda brief dfaescription of function.
C (cfarry) holds the carry after addition or borrow after subtraction.
asdfP (parity) is the count osdff ones in a number expressed as even or odd.
Logica 0 for odd parity; logic 1 for even parity.
A (auxiliasdary carry) positiosdafns 3 and 4.
Z (zsdfero) shows that the result of an arithmetic or logic operation is zero.
S (asifgn) flag holds the aritasdfahmetic sign of the result after an
arithmetic or logic instruction exesdfcutes.
T (trap) The trap flag enables trapping through an on-chip debugging
feature.
dsf
D (direction) selects increment or decrement
O (asdoverflow)
IOPL used in protected mode operation to select the privilege level for I/O
devices.
NT (nested task) flagasdfasdf indicates the current task is nested within
another task in protected mode operation.
RF (resume) used with debuggisdfng to control resumption of execution
after the next instruction.sdfaa
VM (virtual mode) flag bsdfit selects virtual mode operation in a protected
mode system.asdfa
AC, (alignment cheasdck) flag bit activates if a word or doubleword is
addressed on a nonfa-word or nondsf-doubleword boundary.
VIF is a copy of the isdfanterrupt flag bit available to the Pentium 4-(virtual
interrupt)asd
VIP (virtual) provides information about a virtual mode interrupt for
(interrupt pending) Pentium.f
ID (identification) flag indicates thasdat the Pentium microprocessors
support the CPUID instruction.f
Segment Registersasdasd
Generate memory addresses
Four or six Segment resdgistefars
CS (code) segmenfat holds code (prograsdams and procedures) used by the
microprocessorsdf.df
DS (data) contains most data used byas a program.
ES (extra) an aadditional data segmentsdf used by some instructions to
hold destinatsdfion data.fasd
SS (stack) defines the area of memory used for the stack.
FS and GS seasgments are supplemental segment registers available in
80386 – Core2 microprocessor. – allow twoa additional memory segments
for access bdfy programs.
Windows uaasdfses these segments for isdffanternal operations, but no
definition of their usage is available.
2-2 REAL MODE MEMORY ADDRESSING
Real mode operation, - memory, conventional memory, or DOS memory
system.a
Segments and Offsets
All real mode mesdfmory addresses must consist of a segment address plus
an offset address. – segment address, - offset address
Segment plus offdfasdfasset
Ending address
Default Segment and asdfasdfasdfnasdft register defines the start of the code
segment.
The instruction pointer locates the next instruction within the code
segment.asdfasdfasdfasdfasd
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