notes:
we are running in real mode - true addresses (not virtual)
what is a memory segment? ok... 64K group of memory
addressing 0x12340 + 0x0017 = 0x12357 or 1234:0017
12340
12357
1234:acts as last "digit"
fitting more information into the last digit, so spills over.
100:003
1003
but 100:049 = 1049. get it? spills over to the next digits.
addr:offset
addr + offset
far pointer: includes segment offset (so can point to memory outside current reach)
for LEA (load effective address)... does a single register contain the base, displacement
and offset? and LEA does the calculation?
Top of stack at offset SP in stack segment. RECALL that stack grows DOWNWARD
current element at DS:SI, destination at ES:DI. Incremented automatically (if direction flag
is clear. if direction flag set, then decremented).
REP instruction -- repeat number of times in count register
ES and DS are at 16 byte increments... actually address is DS * 16 + SI
segment and offset
CLD - clears something? makes sure direction is increasing
certain restrictions on how far you can jump. if want to jump unlimited amount in a test, check for failed condition (and jump ahead). otherwise, execute next instruction, which is to jump really far.
JNLE NoJLE
JMP target
NoJLE:
This will test JNLE... if false, then exits. If true, then executes JMP target, and jumps ahead (any amount).
